I've had two generations of BMW convertibles and neither have allowed a single drop of water into the cabin. Of course, I avoid high-pressure wash systems like the plague. I know plenty of other owners, and they've had no complaints either. Sounds like you got a car built on a Friday afternoon. BMW should completely replace your seals and fittings.
Good luck to ya.
Past: 2008 M3 (E93) naturally aspirated V8 realness!
Past: 2012 740Li (F02) M-Sport (European Delivery)
Present: 2016 750i (G12) M-Sport