Yep guys! I'm experiencing the same problem too on the passenger side, there's always a messy water there like you can remove the mat on the floor and hold it-up, the mat is very heavy and you can see right away so much water is leaking from it. At 1st, I was a bit worried about this because it seems like it was coming from the thermostat, even I do not have any heater problem. But now, as I read the forum many of you seems having the same issue.

And I'm more confident now, this is coming from the rain instead! I'm gonna try to work on his tail.

(01 X5 4.4i)