First dry the area completely with a fan to prevent mildew smell and allow a neutral test. I would then lay some cardboard over the area. You need to determine if the water is dripping down or soaking up from the bottom. Drips will show splash patterns on cardboard. Perhaps a run through a touchless car wash would allow you to quickly duplicate the source.
By the way have you ever used high pressure washer wands on your X3?
1979 Porsche 911SC
1996 Porsche 993 C4S
2003 BMW M5
2013 BMW X3 35i
Last edited by bimmernut1; 08-03-2013 at 08:45 AM.