Cadillac Jim

The all-electric future is a lot farther away than most realize.  You can't jump in any all-electric vehicle and take a two-day road trip.
Somebody decided to cancel the 4.4 l DOHC Blackwing V8 before developing it to produce 700 hp and remain warrantable to 100,000 miles.  The 6.2 LT is about the same weight and its size is manageable.

There is room for both engine types in autos.  As an engineer, I see turbines as the best technology for long-haul 18-wheelers and even trains, but turbines have obvious carbon-capture problems.  Trains have used diesels with electric motors powering the drive wheels since 1924, and turbines driving the generators are the obvious modern design.  For short trips, stop-and-go, plug-in electric is the obvious choice, with some competition from PZEV turbo four-cylinder engines which have decades of development behind them.  For the near term, I see plug-ins and hybrids as becoming dominant in consumer vehicles that are used in town 99% of the time, combustion engines for commercial trucks that run all day, and diesels and diesel-electric hybrids for long haul trucks.  I don't mention turbines because turbines have never found a niche in the automotive world.  Sports cars are a separate consideration, and there are many kinds of sports cars, so the drivetrain technology will likely fork, too.  All-electrics have the edge in drag racing, for example, and you will not see an all-electric entry in a 500-mile race anytime soon.

Looking at the Cadillac.com first page on the "build and price" pages for the CT4 and CT5 Blackwing, the CT4 uses a twin-turbo  3.6 liter V6 rated at 472 hp, and the CT5 uses a hand-built supercharged 6.2 liter V8 rated at 668 hp, apparently adapted from the Corvette supercharged engine.

The "edit" button has gone away on the post of 9:05 Monday morning.  I think that happens once others have quoted or perhaps "liked" the post.  If you can't re-enable the edit button, please delete the last sentence of the third paragraph that begins "This ...".
I don't think I could help him very much on the basis of the video.  The STS-V and CTS-V are very different cars and drivelines, except for the transmission.  I would start by reading his OBD codes, though; he must have tons of them.  Bruce or other STS-V owners would know more about his car.  His over-the-air fixes were to take effect in late August according to the video, so that would have come and gone.
My main concern on the basis of the videos is that there might have been some overvoltage by a battery charger that damaged some modules, because his touch screens didn't respond; I hope that was for the radio modes only.  That can be due to corrupted software, which may or may not be corrected over-the-air.  Normally, disconnecting the battery simply resets all the modules and you need to re-learn the throttle, timing, and such, and re-set the radio station that you were listening to, but certainly simply disconnecting the battery doesn't damage anything.  The wheel sensors could be missing, have wiring or connector issues, etc.  The TPS system probably has missing tire sensors; some tire and wheel people don't know what they are and will simply throw them away and use new valve stems when re-mounting a tire.

The big items were "Spare Parts" at $2,912 and "Other Material" at $3,782".  The bumper guard and paint are supposed to be $250 or less, but they probably replaced the bumper beam and at least one of the two shock absorbers, which can easily run $3K.  But, another $3.7K for "Other Material" that was not itemized???
A bill of that magnitude from any source must include a full breakdown of all parts, their source, and your cost of those parts.  Some would include manufacturer part number on the parts.  This is very important for Cadillac or any high performance auto repair because many mechanics just call the local parts house and give the make and model, and the parts house will look up the cheapest part that will bolt on in a catalog and neither knows that they have just made the car dangerous to drive within manufacturer's specified performance envelope.  If you have the part number, you can deal with the problem; otherwise, you may not even know about it.  Other mechanics will order the "economy" version of a part and charge for the "performance" version...
Some of the other documents provided by the dealer may have included such lists.  The guy didn't say.  I did look at one other of his videos on the STS-V, and he spends it complaining about problems with the car that he introduced himself by disconnecting the battery and not reinitializing the modules.  GM fixed the radio over-the-air, and that fix may have solved all his problems, but he made the video before the fixes took effect. [...]
BBF, please forgive me for my hard knocks anecdotes.  All of them are from experience, though.

I agree; I wondered if he simply needed to put it in track mode.

Two takes:  The extreme and long-winded rant about the transmission and RPM range seem more to be about how he expects the engine management to work, as in keeping the RPM range high as needed for a naturally-aspirated car or a small engine, AND, brake smoke does not mean that the brakes are on fire, or even that there is anything wrong.  This is a zero review.

The part number you gave for the relay, stamped on it, is one digit short of a GM part number. You say you found a relay on Rock Auto that is the same part; I don't see a relay by itself for the 1984 Biarritz electric seats, just 21-pin combination switch-relays and an 8-pin switch-relay. If you could give us the exact application where the same relay is used, and the GM part number, then we could probably find it for you.
You can also match the relay with another one based on the size, voltage (12 Volts), and number of pins and functionality with pinout. That's a last resort but always there for parts like relays.

The url for wheel-size.com is
https://www.wheel-size.com/
They refer to the wheel size as 7Jx16 ET51.  Their "i" button explains that as 7 inch rims, mounting rim type J (most road cars), and ET51 means a positive offset of 51 mm, which is 2 inches.  That's where I got the tire size, too.  Width is 235mm, up from 225mm for older Sevilles, with a corresponding slight increase in rolling diameter (the aspect ratio of 60% is the same).

morty96 -- you can't tell what's wrong, exactly, from what you say.  If we have the codes, they may be able to tell us what is up.  The compressor may be turned off because  a code has been set that says that the expansion valve or dryer is clogged, for example.  If you have a gauge on it and it is reading 100 psi, it probably doesn't have a leak.  BodybyFisher is right, a can of the correct Freon every year or two may be OK but that's not going to address whatever is stopping your compressor from running.  Possibilities include, but are not limited to:
Electrical problem, like bad compressor clutch ground, Bad compressor clutch, Clogged expansion valve, drier, condenser, evaporator, etc. Etc. If we have all the OBD codes we may be able to eliminate a lot of things or even focus in on something specific.  As BodybyFisher says, get the codes (OnStar, Autozone, whoever), write them all down, and post them all here.

Uh, like BBF needs anyone to back him up, but as an outsider in this thread I do think I have something that might help out here.
Whenever the battery voltage drops below 9 Volts during cranking (or any other time, like sitting at a long light at night with the headlights and A/C running...), some modules will start throwing bogus codes.  At least two of them will throw "Battery voltage low" codes to make sure the tech knows to ignore ALL the codes, charge or replace the battery (or fix bad connections), clear all the codes, and start over.
Things that can cause voltage to the modules to drop below 9 Volts when the battery is new:
Wrong battery -- too small, or one with not enough cranking power; or an ordinary battery when the car is designed for an AGM battery Corrosion on either battery cable connections to the battery Bad battery ground on either the engine block or on the car body Dragging starter or something on engine dragging or seized Battery too cold to start engine easily, particularly while engine is dragging due to extreme cold Engine taking far too long to start for any reason Bad connection or cracked Maxifuse or fuse Bad ground on module(s)

I have the 06 DTS service manual on DVD.  I believe that the question is where the battery grounds are.
From the FSM, the main battery ground cable is G303, "Battery negative cable ground, under the rear seat on the right floor pan" while there is another ground cable wire, if a smaller gauge.  The FSM schematic from starting circuits is attached.
My IE has updated to the point that the GM SI TIFF viewer isn't there anymore.  I'm trying to re-install it...OK.  The smaller battery ground wire goes to the BCM, apparently as a BCM ground.
It seems that there is an engine ground strap, between G110 "In the engine compartment, right side ground strap to the right frame rail below underhood - fuse block", and G111 "In the engine compartment, right side ground strap to the right frame rail below underhood - fuse block".  Since they say "right side" there may be another ground strap.

If you have OnStar, push the black button and ask the lady to read you the OBD codes and write them down and post them here.  You can ask her to email them to you, which might be simpler and avoid an error in writing them down.
If you don't have OnStar, find and Autozone near you and ask them to read your OBD codes for you.
Look at the sticker on the underside of your spare tire compartment cover and write down the RPO codes related to your radio.  I would take a cell phone photo of that sticker, which has all your RPO codes, paint numbers, etc., and keep that photo on my computer for reference.  The radio codes for the 2007 CTS are (this list may not be totally complete because I just now picked it out of the FSM):
UAV    Infotainment System 005.1
U2J    Digital Audio System S-Band, Not Installed
U2K    Digital Audio System S-Band
U2R    Infotainment System 001
U2S    Infotainment System 002
U2X    Infotainment System 007
U2Y    Infotainment System 008
U57    Speaker System 8, Dual F/D Pillar, Dual FRT DR MTD, Dual RR DR MTD, Subwoof PKG Shelf, I/P CTR, Amplif, Bose
U66    Speaker System 7, Custom
We will need that information to get the right schematics in the factory shop manual (FSM).
If you have a Volt/Ohm meter, you can check for power at the radio and a good ground.  Power to the radio is through the RD/WH wire, ground is through the BK/WH wire.  If you have premium audo (Bose, probably) you have the 30 Amp AMP fuse with power directly to the power amp on the RD/BK wire.
If there is more than a small fraction of an Ohm resistance from the BK/WH wire to chassis, check ground G402, which is In the rear compartment, to the rear of the left rear shock tower, below audio AMP.

Just now saw the post.  The problem does seem well in-hand.
I do agree with BBF and others that you need to work with the dealer that you trust or another mechanic.  And, the first thing I would do if the car was mine is get another oil sending unit and ask the service tech to change it with an oil change, which I would schedule as soon as I had the oil sending unit in my hand.

Is this with the front wheels off the ground and engine at idle?  When the wheels are on the ground and you give it a bit of throttle in Reverse, does the car move forward?   Does the car surge against the Park pawl when you give it a bit of throttle in Park?
This is the FSM entry for "Forward motion in N:
Checks
Causes
DEFINITION: Forward Motion in Neutral
Forward Clutch Housing
Feed hole plugged, inspect tower
Forward Clutch Piston
Jammed
Forward Clutch Plates
Seized or jammed
Forward Clutch Springs
Jammed
Forward/Coast Clutch Support Hub
Holes plugged
Manual Valve
Mispositioned or stuck
Shift Linkage
    •  Mispositioned     •  Disconnected The only do-it-in-the-driveway DIY check that is listed is to check the shift linkage.  The FSM drawing of the cable attachment to the transmission:

1 - where the cable attaches to the transmission.  This may be disconnected in your case.
2 - cable holder, with adjustment.  The FSM adjustment process follows.
Range Selector Lever Cable Adjustment Notice: Adjust the shift control cable only while the transaxle and the gear selector are in NEUTRAL. Failure to do so may cause mis-adjustment.

 
Set the parking brake and chock the wheels. Remove the shift cable terminal from the transmission manual shaft lever pin. Pry on the shift cable terminal at the manual shaft lever pin with an appropriate tool. Prying or pulling up on any other part of the shift cable may result in damage to the shift cable .
Fully lift the adjuster lock button. Ensure that the adjuster is free to move. Place the transmission manual shaft lever in (N) Neutral. In order to find (N) Neutral, rotate the lever fully counterclockwise to (P) Park, and then clockwise 2 clicks into (N) Neutral. Place the gear shifter inside the car to the (N) Neutral position. Use the transmission shift indicator on the console to find (N) Neutral. From under the hood, grasp the shift cable terminal and pull it toward the pin on the manual shaft lever. The shift cable adjuster spring should compress as the terminal is moved toward the pin. Attach the pin to the lever by pushing down carefully until it snaps. Do not pull the terminal beyond the pin and then push back. This action could move the shifter out of (N) Neutral.


Press the adjuster lock button down flush with the adjuster body. Shift to (P) Park and release the parking brake while applying the service brake. Start the engine and assure all of the indicated gear positions match the vehicle response.

Don't give up if the fuses don't do it.  We haven't checked the grounds and connectors yet.
A dongle with BlueTooth with included laptop or cell phone application will do the trick.  I use OBD Link from ScanTool:
https://www.scantool.net/
The included software/app will do to get started.  I use the pay version with the GM data add-on.  The $80 package, with your existing laptop, will pay for itself in the first 45 minutes of dealer tech time.
 

The fact that the idler sprocket mounting bracket seems to have been forced to the right to pull its mounting bolts - see thread damage in photo in post above - it seems possible that the first failure was one of the cams locking, which would happen when a few teeth were skipped on that cam.  When all the parts are out and examined, we may be able to tell what the first failure was, and why it happened.

All modern engines are interference engines, and if a valve is standing fully open and the engine is turned, the piston will hit that valve.  If the engine has not been turned, it is probably OK.  The starter is strong enough to damage the engine if a valve is standing open.
If the engine was apart and not running when the problem occurred, you may be OK.  If it was running when the timing failure occurred, then, as KHE says, you will have damage.
As KHE says, this is a "very unusual failure."

I believe that the axle housing with extension is available from GMPartsDirect, but not the extension alone. The price is steep.
I would make sure that you do indeed need the housing. A bad housing is rare and probably most are due to collision damage. If it's just the rubber donut or bearing, you are in for a lot of trouble and expense because it seems that that the extension housing doesn't sell often.
Frustratingly enough, the parts page for the group "UNIVERSALS AND REAR AXLE" doesn't have a parts diagram. The bare differential case is listed under rear suspension as well at $126, but they also list an Axle Housing for $567. Without a parts diagram I can't tell.
Most other GM dealers that sell online use the same catalog software so I don't have a lot of hope that the parts diagram will be on another site.
You might try Rippy Automotive. The head of the parts department there can get anything that exists.

That platform was sold for various cars in the 1976-1994 time frame as follows:
Chevette (US, Latin America, Chevy or GMC) Pontiac Arcadian in Canada Pontiac T1000 or 1000 (USA, 1981-1987) K-180 in Argentina Vauxhall Chevette Opel Kadette Isuzu Gemini Holden Gemeni (Australia) Chevrolet 500 pickup in Latin America through 1994 Grummett (station wagon or pickup, Uruguay) See Wikipedia article:
https://en.wikipedia.org/wiki/Chevrolet_Chevette

Some come with the F45 suspension and some come with the F55 suspension with the magnetic shock fluid. The 2003 Seville comes only with F55. If the F55 system can be fooled with the same 4.7K resistor as the F45 suspension, that is something we need to keep handy.