Is it the car rebelling against the bow tie powerplant? Perhaps leave some of the old engine parts in the trunk, so it does not get lonely for German Engineering?

Otherwise, I have always shot some light oil into the balls for the check on the door stop. The replacement should only be about $20, and a quick repair, if it is like my 560SEL.

good luck!

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1989 560SEL (172k)
1989 325IC (122K)
2004 Suzuki Volusia LE (3500 miles)
2005 Yamaha Road Star (20 K miles)