I just rebed my frame this spring as it was also leaking. You propably wont be able to use buytl on it because of the way it fits will require a liquid sealent (mine did).
While it was off I soda blasted the frame to remove everything, and sanded under the frame. I then rebed it with 3M4000UV, and put a bead of it around the outside edge as well to ensure a complete seal. Will post a few pictures later when I'm not on my phone.
I found once the frame was out most of the screw holes were compromised and had some rot, and there was a lot of leaking I wasn't aware of. I filled in lots of the frame with penetrating epoxy, about 2 cups worth of epoxy went in. Overall it took me about 3 or 4 weeks (working on weekends only, usually only one day) early spring to get this issue fixed.