WELL-MAINTAINED W126's are the best.
and the pre-1988's are to be preferred as they only had a driver's side airbag, therefore also a glovebox.
my 1986 560SEL is my favorite. bought it new. it has 250,000+ miles. interior still looks like new. exterior could use a new paint job. basically front end chips from rocks and bugs. a few months ago i had it de-dinged by a master of paintless dent repair.
probably the cheapest car to operate over the long term. irreplaceable. nothing like it made today.
i also have a 1987, 560sec. another great merc. also bullet-proof mechanically.
lately though, with the cooler weather in houston, i have been driving my 1995 e320cab. a great little car.
my advice is that when you find a w126 vintage 1986-1987 with full records and one owner, try to get the owner to hold the car for your purchase until you can get it to a good indy garage. get the car up on a lift and go over it carefully. get an estimate for repairs.
if you are really paranoid, take it to a second indy for a similar inspection.
in closing, my old 560sel would be tough to sell for $5,000. on the other hand, to me it is still worth what i paid for it new. principally because there is nothing better than it on the market today. nor will there ever be. these were the last of a very special breed of automobile. daimler chrysler will never create its equal.
a votre sante