My car idles very roughly at first starting in the morning, it is fine after that. I took it to a GM dealership, they said it was 95% that it was a head gasket that was the problem as coolant was in the # 1 cylendar. They recommended a Cadillac repair facility. How much should this repair cost ? Can a GM facility do the job and if so, what are the negatives and positives vs a Cadillac repair service ?
Sounds like you have some very serious issues. Cadilac introduced the aluminum engine in 1982 and uses it to this day. These engines were light and great for performance and economy. The only problem Cadillac did not warn about (GM made billions on parts and new engines) was this engine could never be overheated, even a little bit. By the time the hot light came on the engine was literally self destructing!!1
I use this analogy that some people that have done this understand. You have a bonfire. You throw an aluminum can into it and watch it melt in seconds, not from the flame, but the heat. This is what happens to one of these engines running hot! The aluminum engine is not at all like my big Chevy 454 made of cast iron or my wife's Navigator with the 5.4 triton she did peg the hot needle on, again, cast iron. In her case, she let it cool down, we threw coolant in it and it was good to go. Your car cannot get away with this because you have an aluminum engine.
Now, you ask on pricing and dealer v service center. Here is what you need to understand. The blown head gasket is an effect of over heating and never the cause of it. Here is your problem and it is very dire. At this moment until the engine is torn apart, no one knows if this is a head gasket problem or a cracked engine block. it very well could be either. Personally, I would never consider a dealer for the diagnoses and engine work. You are paying way too much at the dealer and there are many competent technicians at the bigger service centers.It's bad enough Cadillac made money on this crappy engine and it is like salt in the wound to take the car to be repaired by them. I am very concerned for you and hope all this is, may be just a head gasket and before it leaves the service center, the real reason for overheating must be found or you will be right back at the service center in a half hour with another blown head gasket. I kid you not!
You need to hope and pray the engine block is not cracked exposing an open cooling jacket into that cylinder.
Unfortunately, it gets worse from there. There is about a 0 chance you will find a used engine that hasn't been overheated and that is why the car is at the junk yard. Recently a person wrote me that he was getting an engine from a pick and pull junk yard. I told him this was not a good idea if he couldn't let the engine run and doing a cooling system pressure check before the engine was started. It is pretty sad that one can't find a good used engine for any Cadillac, but it does demonstrate my point as to how common this issue is of overheating. Those people must have been laughing all the way to the bank because the only way to solve the problem was with a brand new Cadillac crate engine for $4k.
If the block is junk, here is one option that will be expensive, but not as expensive as a Cadillac crate engine. I would search the web locally or nationally for engine rebuilders that have remanufactured engines with a guaranty and you might save money and that would be your only option. One such company I can think of is Jasper. I am just giving you worst case scenario because until that head is removed and the cylinder areas inspected, no one has a clue as to how bad the damage is and don't go to a dealer!!!!!
Jeep was forced to put a big orange sticker on the dash to warn it could roll over. If Cadillac actually cared about the owners of these cars, they would have placed a sticker warning this engine could never go above 220 degrees or past the 3/4 mark on the gauge because of guaranteed engine destruction!
Let me know what happens when you find a shop that can tear down the engine. If you are lucky, it won't be a cracked head or cracked block. Prepare for the worst and hope the best. All I am doing is warning you of all the pitfalls with this engine once over heated. I have even seen pistons begin to melt with these.
In the 80's Renault with AMC made the Alliance and the Encore with the aluminum engine. The engine was a aluminum engine and overheating damage was so common that they actually made a piston liner kit where you could literally install new piston walls and pistons that slid into the block! These cars were in the shop all the time from over heated engines and we could not warranty overheating damage. The point being that at least they made a repair kit and Cadillac didn't. These Renaults were driven so hot that the connecting rods were dripping the aluminum off of them! Your Cadillac aluminum engine is melting when it is overheated. These engines do not blow head gaskets for any other reason.