I just got done with a very annoying ordeal...the passat got a rock crack and I went to have the windshield replaced. It didn't sit completely flush but the guy said that they put a large bead of glue that waterproofs it. A month later, the car's horn starts beeping and the instrument panel goes nuts, the car stutters. Something is shorting. It turns out that the relay panel under the dash is soaked and the floor is wet. Another windshield later, the passenger side is soaked. I go to get the cabin pressurized to spot any leaks and the guy changes the windshield again. Another windshield later, the driver's side is so wet that the "A" pillar is visibly wet on the inside trim. The 4th windshield, the manager uses a machine to pressurize the cabin and it has horrible leaks. The manager scraped out all the old gasket and put a new seal and this time it's 90% flush. I will go back once the gasket is completely cured and it should be okay this time. So if your passat windshield isn't almost completely flush with the A pilar like the old one, it'll leak. They'll tell you that they put a large bead of sealant so it can't leak...but it'll leak. Or at least go back and have the cabin pressurized to test for air leaks. If you suspect the sunroof drains, open the sunroof and pour water into the corner drains. The in the mk3, the drains are inside the metal A pillar and empty in the front fender. Then the water dripples out the front wheel well. In the mk4, the drains empty out next to the door hinge.