simply remove the door panel, it takes a minute or 2. once removed you will probably either see the vapor barrier torn or the bottom of the vapor barrier is not sealed to the body of the car with the butyl tape.... or both. dont waste your time repairing the barrier... becuase if you did a poor job, you still going to have a leak. Invest the 30 bucks or so to get a new barrier if its torn. dont reuse the butyl tape either, take a few minutes and remove all of it. if your a or c pillars have water stains on them, your sun roof drains are clogged... probabbly wouldnt hurt to clean those out while your out there anyway.... if you took it to the dealer, you are looking at a minimum of 2 hours.. or thats what I would charge.. ... 135/hr to boot.
clint