Anyone that has a sun roof/moon roof needs to know they do require maintenance. If you park outside its even more of issue. You should at least once a year open if completely and then get out of car and check for debris in the channels. It doesn't take much. You could open it one day and a small leaf could get in and you may not have noticed until it rains. It only has to be vented for this to happen. If the channels are kept clean a sunroof leak is very rare.