I had the same problem a few years ago on my '93 190E. It turned out to be a defective sub-frame mount. When I removed the right rear wheel and lifted the suspension up with a 2 x 4, I could see play in the sub-frame mount. The rubber bushing was worn out. I changed it myself and no problems since.

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible