I've done a lot of research and looked at many S500 coupes before I bought mine last fall: 1995 with 41K miles. While searching I realized that it doesn't matter that much what year it is. It's all about the miles and the previous owner. If the previous owner took good care of the car then you should be safe buying it. The guy who drove my car before I got it took really good care of it, it was very clean.
But then couple of months pass and my friend tells me something that made me very sad!! He saw a 1999 CL500 with 50K miles go for sale at the auction for $29000. I WAS SO MAD!!!!