I can't believe this! It rained really hard last night and today my leak was still there!
The water is dripping from one corner of the vent fan housing. I don't think there is any way it can be getting past all the sealing that I did, so it is either blowing into the top of the fan or coming in somewhere else and "migrating" to the fan housing!
Hopefully it will be dry enough I can get back up there tomorrow and look for another source for the leak!