Sorry to beat a dead horse here, but I just tried to seal the mast of my new (to me) h16 and it wasn't that obvious if I was actually sealing anything or not. The whole process was much clearer to me before I had seen the top of a mast.
So - do you have to take the end cap off? or just slather 5200 around the edges?
Sorry to burden everyone with this - I hate turtling, and the guy that owned this boat before me said he used to turtle it all the time.