It's part of the door switches driver door. It comes right out with a plastic trim tool.
Beware a handful of stuff goes through the box so door locks for example won't work properly when it's unplugged.
A buddy that had the same problem found his old switch and took a picture yesterday. This is what it typically looks like.
I charged him $50 to repair the switch. You can try to buy a used one but that's what he did and just bought another with the same problem. Apparently a lot of previous X5 owners use driver through without awning or something.
Cut a hole to let water drain out. I did this with both mine and wife's X5 preemptively when I had the door apart for lock or handle repair.