I had similar problem with my driver side door. Had to slam it in a very un 126-like manner in order for it to shut. I lubricated the door lock using silicon lubricant. That fixed the problem. The door now shuts like it's supposed to shut, gently with that characteristic thump.

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Riadh
'89 560SL Rauchsilber
And what is good, Phaedrus, and what is not good -- Need we ask anyone to tell us these things?