The drains to the sunroof become clogged and can cause the sunroof to leak rain water into the vehicle cabin. There are rubber "pinch" drains that emerge at the drivers side doors. The drains become clogged at the pinch point with debris and that causes rain water to back up all the way to the sunroof and then spill over into the cabin. All you have to do to fix this is cut off the pinched portion of the rubber so that it drains properly. VW is now aware of the problem and there is a recall campaign. VW fixes the problem just by modifying the pinch point of the drain.