I also pumped nearly an entire tube of Dicor all around my fan. I didn't want any leaks.Me too, but I also tend to go overboard when I'm uncertain and doing something new. There are lots of ways to do this job. But the goal is always the same - secure at highway speeds with no leaks. I used a plastic outer adapter from Hein and made my own inner adapter from wood to mate with my ceiling contour. I used butyl tape on both sides of the outer adapter and a little construction adhesive to hold the inner adapter against the ceiling. But then I went overboard with the Dicor and emptied a whole tube around the base of the fan. Not pretty. In hindsight, I could have just covered the screw heads. The perfect contour of the outer plastic adapter plus all those screws into the inside adapter created a very uniform, tight seal with just the butyl tape. Even better would have been to follow Hein's recommendations and seal the outer adapter to the roof with Windoweld.
FYI everyone, exposed butyl tape dries up and cracks over time. Not an issue for thin sandwiched applications, but don't leave thick build-ups exposed. DAMHIK
Thanks for the note on the butyl tape drying.
Related, I feel that due to the elements, a fan installation should be inspected regularly. The sun is very harsh. I suspect that even the Dicor will need to be peeled off and a new slathering be reapplied should it ever dry up. It reminds me that I've not done that this year.