The one and only owner should have all the service records and these
should come with the car if you buy it. At 7.5K mile oil change interval
- if that's what it is - there should be 20 oil and filter changes - are
there? Do a similar check with the transmission.
You basically want to determine if the car was maintained as it should
have been, for the basic components will last a long time IF, BUT ONLY
IF, they're properly maintained.
If you buy a M-B, find an independent shop to maintain it or learn
enough about the car to DIY. Don't take it to a dealer for they always
want to sell you something - repair a small oil leak etc. And always,
always ask the cost before authorizing work or you'll learn first hand
the cost of owning a M-B.
Repairs come in bunches so keep a $2K repair reserve on hand.
Good luck with your quest.
P.S. Look at a few E320s - 24 valve six - unless you really want the
extra power of a V-8.