when you're talking 97-98 models that have been in service for nearly a decade, I'm not really sure the traditional "transmission issues" (with regard to prematurely-failing components) are a factor. If they've survived to this age I'd be more concerned with maintenance, such as the trans fluid/filter changes (if they've had one) and having the adaptation values, etc, checked out on the trans by a dealer or good indie. Either way, it's hard to pass up a later-model at the same price as an older one even if you are talking V6 vs V8. Of course, at either age and mileage, you're going to be looking at suspension bushings and possibly a head gasket in the near future. On all these models, oil change history is very important, as the 1998-up went to the FSS system, and I'd be inclined to choose the 97 if it's oil was changed every 5-7k rather than a 98-up with oil changed done at 13k. Just my bias.

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former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL