I actually did look in the inside a couple days ago when I looked into my window failure. I did not see any rust on the inside but did not look very close. Soaked it all up with WD40 for now.

But to clarify, the rust is above the trim. Above the fold in metal. So about a half inch or more from the plastic skit. I will take a pic.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car