It also helps to know which generation 300D you're talking about. Is this a W123 300D? A W124 300D with the 3.0L engine? W124 300D with the later 2.5L engine? Different generations have different things to watch out for and different suspension designs and drivetrains. Knowing which one you're looking at helps to focus the conversation.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)