The suicide doors on the 170SD are of a different variation of what you're probably thinking of. You're probably thinking of suicide doors like the Lincolns of the early to mid 1960's. I'll post two pictures, one of a 170SD, and one of a 1965 Lincoln Continental so you can compare the doors. First, the 1965 Lincoln.

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.