I recently traded mine in. It was my third BMW vert and my first hard top. It never leaked until it was damaged after being rear ended. It was repaired correctly so that it sat properly on the car, but the seal wasn't installed fully flush. The leak was pretty bad at first and I brought it in for repair, but they couldn't fully stop it. Water would pour in if it rained more than lightly. I eventually learned how the roof is sealed and fixed up most of the problems. After that, it only leaked if it sat in heavy rain. It never leaked while in motion.
The main issue is not with the front seal or with how the windows sealed on the sides. It was the gasket under the roof that wasn't seated properly. Water would collect in the railings until it got back to the spot that wasn't sealed. I'm pretty certain it could have been 100% fixed if I had tried. I never gave it a lot of effort. Don't expect the dealership to figure out your leak if you have one. Almost none of them have body people capable of figuring it out. If it doesn't throw an error code, you will almost always get the famous "unable to reproduce".
That's not to say that 100% of shops couldn't fix a leak, but most of them don't employ body people. They are technicians, not body repair, but unfortunately roofs are not repaired at the body shop. They have specialized tools to align them and it takes specialized training to use them, which is a technician's job in BMW's eyes. The body people are usually in a different location. Occasionally you get lucky, though, and find someone who understands how the seal is supposed to work. Knowing what I now know about the way the roof is sealed, I wouldn't be concerned. However, if you're irritated easily and not mechanically inclined, you could be in for a world of frustration.
