QUOTE(Mikey914 @ Sep 2 2022, 11:51 AM)
I made a replication of the 75 barriers I had. Anyone have pics? It should be simple, just haven't see a "flap" before.
If you have this much water inside your door, it may explain the rust in the bottom channel. My understanding was it was like a house. Cold outside warm and humid inside (if you actually drive it in the winter). The vapor barrier would keep the warm air from being cooled by the metal on the door.
I'm not saying the flap is important, I just know it was on all the barriers I've seen (which isn't that many) so I replicated it when I did mine.
But to your point. I think it is more about controlling condensate/dew that forms inside these metal cavities when the car sits at dew point in a humid environment - plus any water that leaks past the window squeegees in the rain. Given that the other side of the vapor barrier is against fiber board prone to water damage, I can see why the Germans got picky about this. But if the car has your plastic door cards, it would make no difference since they won't be water damaged.