Let me add another bit of information that I haven't seen yet in this thread as well as giving my own opinions ...
The OM617 engines will require that the valves be adjusted every 15 K miles, as opposed to the OM603's that don't.
My 300SD has given me six years of faithful service, and I've probably dropped maybe 4K into it on top of the 5K or so that it cost me...
A couple of $1K jobs at the indy, and several $200-600 jobs. I don't count things like tires and fuel.
In my experience also, the W124 body style is much more troublesome and expensive to maintain than a W126.
My ideal car would be a 1985 300TD wagon, with an 86-87 SDL second... but I'd also consider a 1987 300TD wagon. Call me a glutton for punishment but the W124's handle a lot better, at least in terms of agility, than either the W123 or W126.

__________________
Bob Roe
Lehigh Valley PA USA
1973 Olds 88, 1972 MB 280SE, 1978 Datsun 280Z, 1971 Ford T-Bird, 1972 Olds 88, 1983 Nissan Sentra, 1985 Sentra, 1973 230.6, 1990 Acura Integra, 1991 Volvo 940GLE wagon, 1983 300SD, 1984 300SD, 1995 Subaru Legacy L wagon, 2002 Mountaineer, 1991 300TE wagon, 2008 Murano, 2007 R320CDI 4Matic 52K, some Hyundai, 2008 BMW 535xi wagon, all gone... currently
2007 Honda Odyssey Touring, 2014 E350 4matic

I love that color... actually I love blue MB's in general.
If it were me, I would personally fall in love with the car, and buy it regardless of condition. BTDT
My advice to you would be to have your mechanic give it a good Pre Purchase Inspection... the $50-100 that it would cost would give you a good idea of what you're getting into...

__________________
Bob Roe
Lehigh Valley PA USA
1973 Olds 88, 1972 MB 280SE, 1978 Datsun 280Z, 1971 Ford T-Bird, 1972 Olds 88, 1983 Nissan Sentra, 1985 Sentra, 1973 230.6, 1990 Acura Integra, 1991 Volvo 940GLE wagon, 1983 300SD, 1984 300SD, 1995 Subaru Legacy L wagon, 2002 Mountaineer, 1991 300TE wagon, 2008 Murano, 2007 R320CDI 4Matic 52K, some Hyundai, 2008 BMW 535xi wagon, all gone... currently
2007 Honda Odyssey Touring, 2014 E350 4matic

Hmmm. The auction says it's silver, but it looks like a light blue metallic on my monitor...