Call the Parts Department at your local MB dealer. The part should be available in a day or two. Better to use a new part than have a repeat with other used parts from a salvage yard. Getting back to your door adjustment ... can't imagine that the previous owner would have compensated for slightly sagging doors by adjusting the windows. Perhaps you raised the doors too much. I recall making a slight adjustment to the fore/aft position of the driver's door on our 1991 300CE and the window was fine.

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Fred Hoelzle