I own a 2005 X5. It has a little over 12K miles on it, and has been well cared for. Just before Thanksgiving it rained and lo!...the rain came in. My BMW dealer was great. They took it in on an emergency basis, and after 4+ weeks they got a replacement sunroof cassette, which they installed. The Service Dept told me that the problem is not uncommon, and the factory has developed a new fix which requires replacing all hardware.

Fore-warned is fore-armed! In case it happens to your X5, don't let your dealer tell you that your car is the only one in the world that this has happened to.