Did this on my X3, thought I'd share it with X5 guys.
Noticed a wet carpet in the rear seat on the driver's side.
Opened up the door to inspect.
I verified the door drains were clear.
Used T30 to remove 3 bolts.
You must use extra long Torx bits.
Popped off door panel
3 clips to detach.
Resealed the hole with gutter flashing caulk
I keep a tube of this for resealing vapor barriers after window regulator repairs
GooGone helps clean up any mess.
https://www.amazon.com/gp/product/B000DZBFRE/
Pics include the leaking area.
My bowden cable door handle got detached so I took a photo of how it goes back.
If anyone ever has questions on this repair, let me know.