Love the Ride
Reminds me of my last BIG Cadillac, a 1974 Talisman. What I have found to work on the GM cars is Brasso to cut the oxidation. I'm not sure when they changed the paint, but I believe they used lacquer based paint. On my old cars I too tried every automotive product under the sun, until I tried the Brasso. A small amount on an old towel, rub it on the paint, don't let it dry like wax, just keep polishing the paint, changing to some fresh toweling as the oxidation comes off. Be very, very careful and just try a small surface first. You can get carried away and remove too much paint. If you find it works ok, then do a small section at a time, say the trunk lid. Then follow up with a good regular car wax. I currently use Eagle One Nanowax on the Mercedes. It has been two years and the wax is still holding up and beads water.
Back in the early 80's I bought a 1966 Brougham and initially thought the car was silver, the paint was so bad. After a can of Brasso and some wax, I was able to restore the paint back to the original gold color.