Dave, if it's an '85 it's a W123 coupe, the generation sold in the US from 77-85. BTW, is it right hand drive (UK model) or left hand drive (Euro)? Here's a couple of associated W123-specific sites that you'll find more info. at:

http://groups.msn.com/W123Club
www.w123.net

Also try the "Vintage Mercedes" and "Featured Cars" forums on this site; they cover cars built before and after 1979, your generation overlaps both. You could also post questions in the "Diesel Discussion" forum on this site; most of the W123s sold in the US were diesels, and there's a lot of W123 knowledge in that forum. In particular, posts on the 300CD will be useful; that's the turbo-diesel form your coupe took in the US. For technical questions, post in "Tech Help". You'll get more feedback in any of those than you will in Open Discussion.