BMW Repair: water leaks after driver side window regulator replaced, 3m products, water leaks

Question
Evan, thanks for taking this question. I replaced my power window's relagulator 2 months ago. It was fine for about 2 months and now started leaking water into the footwell in the rear. You mentioned this in one of your postings. Could you please elaborate in detail how to fix this problems? Thanks in advance.

I did use new sealant(black tar rope) to encircle the whole rim of the insulate.

Answer
Jian, the vapor barrier must be torn because the footwell is exactly were they leak when they don't seal. Make sure they are not torn. They are only $20 dollars U.S. new. Please remove door panel and double check your works. You should be able to pour gallons upon gallons of water down a closed window from the outside and have the water drain at the bottom of the door. If the water comes out between the door and the door panel then the vapor barrier is leaking. You can do this as a test on your suspect doors. We use 3M products window ribbon sealer to seal the foam barrier.
-Evan