TOM: There’s no way to completely seal up the sunroof, since it’s essentially a hole in your roof (although factory sunroofs tend to be better than aftermarket ones). So all sunroofs have channels that drain out whatever water does get in there.
RAY: There’s one channel on each side of the car, and they run along the edge of the roof, and then down through the roof pillars and onto the ground. Your channels could be all plugged up.
TOM: The water that sounds like it’s sloshing around in the passenger door could be sloshing around in the A pillar, which is the roof pillar that runs along the edge of your windshield.
RAY: And, like water in the door, if water builds up in your sunroof channels and has nowhere else to go, it looks for the easiest path to the ground — which happens to be through your rear carpet.
TOM: Those channels can be checked and blown out with compressed air.
RAY: If that’s not it, another thing to look at are the seals around the doors. If the weatherstripping is damaged or dried out and cracked, a surprising quantity of water can get into the car through the edges of the doors — and that also could end up on the floor in back.
TOM: The same is true for bad molding around the front or rear windscreen.
RAY: And if it’s none of those things, and you run out of ideas, think about just opening the sunroof when it rains. Maybe getting all that water right on your head can at least momentarily soothe that dry-skin issue?
TOM: Don’t be offended by my brother, Bill. He just tries to look at every GTO as half-full (of water) instead of half-empty. I hope you find the source of the leak!