Ha, based on your thread title, I was going to say..."well answer the door".

Check all the suspension bushings. It might be a good time to start replacing them all little by little. I am chasing similar issues and starting with the differential bushings and lower control arms on our '87 W124 300TD.

There is a thread to this effect about a W123 I believe. The process is the same, parts most likely different.

This can be tedious patience testing work, but the pay off in improved ride quality is worth it.

best of luck.

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85 300D 3 pedal. Current project.
83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.