Going backwards just a bit, I mentioned above that I started re-installing the rear windows. Before doing that, I had taken things apart and totally cleaned everything and re assembled with Mobil 1 synthetic grease in the channels. I also replaced the tired original motors with fresh(er) ones from an e28.
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One problem I ran into is that the glass is secured to the mechanism with two M6 bolts going through a rubber pad. And there is a plastic "grommet' which by now has completely perished. @deQuincey had suggested a few options but I did not have any suitable material. Until I found a piece fo garden hose which was strong enough to cushion the glass from the contact with the bolt but it was a little too big. So I cut it down to size and it fits perfectly.
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One problem I ran into is that the glass is secured to the mechanism with two M6 bolts going through a rubber pad. And there is a plastic "grommet' which by now has completely perished. @deQuincey had suggested a few options but I did not have any suitable material. Until I found a piece fo garden hose which was strong enough to cushion the glass from the contact with the bolt but it was a little too big. So I cut it down to size and it fits perfectly.