Resale on the TDI's are much better than any Mercedes (although the MB diesels tend to depreciate less than their gasser counterparts). Many people have bought TDI's and sold them for close to what they paid for them. They are just very girly looking imo.

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2005 SL65
1999 E300
1995 E300
1994 SL320
1988 560SL
1987 300TD
1982 300D
1955 300SL