I've been looking at a Mercedes on CL. The pictures show a lot of "fog" on the upper surfaces of the paint. My understanding is that if it is single stage paint, it can probably be buffed out. But a clear coat means a paint job. Does anyone know what the '83 MB used?

My memory recalls enamel back in that era.
It should rub as long as there's enough material remaining.

Europe got onto the 2-stage paint before the US did, I've been told around the late 70s.
Originally their clear was like a varnish and would blister.
Then it was an acrylic enamel.
The test for single vs 2-stage was rubbing some fine sandpaper on it:
White transfer = clear, same color as the paint = single stage.
Problem with that is nobody's gonna let you do that to their car.
The fogginess could be the beginning of clear coat failure, before it starts to blister & peel.
Plan on it needing paint - or, you could do a wrap if the surface is perfectly smooth.
The more metallic a color has, the less receptive it is to cutting & buffing as far as bringing back color & depth.
Silver is about as metallic as colors get.

Prior to 1986, all colors were single stage as far as I know, 1986-1991 things started to mix. 91-95 all but black were clear coat, and 95+ all had clear

This what I have been told over the years

currently own

1980 240d - marina blue - single stage
1983 - 300cd TD- light ivory - single stage
1985 - 300d TD - light ivory - single stage