Narrowing down the search parameters would be helpful. I'd say it's likely a local and not likely someone from an upper class neighborhood. So once you've called the tow companies and viewed the impound lots, a drive thru the likely neighborhoods within a 10 mile radius or something like that looking for other models of Mercedes diesels in the driveway might yield some results. You may also look for anyone selling any old Mercedes diesel parts or cars and drive by their house. If you have drive thru liquor stores in your area, showing the picture to the clerks might also work.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13