I had the rear window channel on my 1983 300CD rebuilt at a body shop because of the usual rust-caused leak. Since rear windshields for the coupes are scarce in the extreme, I asked them to have a local glass pro R&R the glass.

I bought a new gasket from whatever source I could since there is little to no choice. It was probably a URO. In any case it was about 4 years ago and it went well. I simply do not have the courage to DIY such a job.