Further info:

Owner (long-time friend) says he had the "rear seals" replaced several years ago, but nothing else has been done other than routine maintenance by MB of Danbury CT, which seems to have a good reputation.

It's a one owner car with all maintenance records. From what I've read on several MB forums, the "new generation" 4matic adds 200 lbs, but doesn't affect mpg all that much, tho' it's still "around" 20mpg. I can live with that for the "big trip" I'm planning. It's his wife's car, so he got the 4matic for her winter driving.

Tom