In addition to the source Bacchus mentioned, look closely at the windshield-to-cabin seam. Also look at the portlight rubber seals. I had a leak coming through the Bomar hatch in the cabin top which was quickly taken care of with a very thin line of 3M 5200 made possible using tape on either side of the joint between hatch and deck. You almost have to be there while it is raining to find these sorts of things.