[bstark]

Wally: This has been discussed waaaaaay back. The fan indeed does not link directly to the vent cover about a foot from it on the roof because there is insulation in the way.

You need to take the caulk "bung" out of the screw hole and remove the screw holding the round cap cover on the vent stack on the roof and look down the pipe and you will see the insulation. Take a sharp hobby knife and carefully cut through that insulation (it helps to use a piece of coat-hanger bent into a hook to pull up on the insulation while cutting) to produce a hole about 2" in diameter through the insulation. Now you can remove your fan as you've done before and explore rearward (towards the lounge) about 10" or so and locate your hole and the vent stack.

I used a plastic container for water of the 2qt variety and sliced it in half to create a "duct" to slide up in the roof through the hole for the fan body to hold the insulation up out of the way between the fan and that hole and allow air (especially moisture laden air) to escape without saturating the insulation.

While you are doing all of this and poking around up there, you will very likely find the source of your water incursion, most likely from the cover screw not being caulked or the roof joint for the vent stack not having all of it's screw heads covered with caulking.

Good luck.