A few years ago I bought a 70 Beetle with a sunroof for my wife (The one that ended up with a pink engine shown on my Yahoo Photo Album). The gear mechanism for the sunroof was long gone and not available for replacement, so you had to slide it open and closed by shoving it. No problem. Soon after buying it we had a huge nightime Florida thunderstorm deluge. No problem, sunroof was closed. Next morning, got in the car, started it up, slid the sunroof open and BACKED down the driveway to the street (the driveway has an incline down to the street. Once on the street I have about 30 feet to go until I have to stop at a four way intersection. Made it high and dry to the intersection until I put on the brakes. Front end naturally dips downward at that point and suddenly a huge amount of water came down on my head, shoulders, down my back...I was totally soaked. It was about 3 gallons of water. *&@#*&^%@#^%&%&^@#*@%&$.!!!!
What the ___k??? Headed right back to the driveway. Changed my clothes, and checked out the sunroof. Found the forward drains and unclogged them. Couldn't find any info about the existence of rear drains, but after a week I located them. Totally clogged too. Water would build up in the back well where the sunroof retracts and stay there. The curve of the Beetle's roof is quite severe, so it would hold a lot of water towards the back. Only braking allows it to sloosh forward.
Well the VW is gone now too. She wanted air conditioning, so I finished fixing it up and sold it for a profit. Then bought some more MG parts with the proceeds.