This was a huge problem with the first gen X3. I had water accumulate in the floors of the car each time it rained. BMW unclogged the drains, but the problem persisted. Long story short, after reading about the "sunroof cassette" on multiple forums, I took it back to BMW. The car was already out of warranty, but the service manager pitched my case to BMW after I showed him online that this was a major problem, and BMW ended up paying for it as a "courtesy". The whole inside roof and supporting panels had to be removed. Total billed by my BMW dealer to BMW was almost $5,000 for parts and labor.