I looked for a year (!) to find a good (no rust) diesel MB in Saint Louis. I eventually put a wanted ad in Craigslist for a diesel MB, and got a bunch of responses, and narrowed down a list from there. I bought a 1980 coupe with 122k and no rust for $5000.

Ironically, my favorite model and color combination diesel MB was the first one I looked at (a 1980 300sd green and tan, original owner's son, all records, no rust, 200k miles for $2300) but I couldn't buy it at the time. I would put an ad on craigslist in the wanted and cars&trucks section(will probably get flagged) and see what responses you get.

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1980 240d
1999 SL500