I had the same problem a while back. The little hobie bracket they give you with the boat to step it where you put the two pins through and all that is a little bit off. With mine I always had to really work it around to get the pins all the way in because it barely fit. then when you start to tilt the mast down, in order to get it to come all the way down you have to actually pull it up and out a little bit. This isn't a problem if you're doing it by yourself, but I had one guy letting out a rope tied to the front stay and me on the tramp so that way we wouldn't drop it by accident. Since all his force was pulling the mast base down and forward, i couldn't get it to pop up and back and the base thing got stuck in the joint and wouldn't tilt all the way back. The mast still did though, and it sheared all three rivets. Then the mast didn't completely come off the base luckily because it was stil being pulled down towards it. I still haven't bothered to fix the problem because as it was already mentioned here, the mast is usually under compression and doen'st even need those rivets. About sealing the bottom though. If you flip the boat the tip of the mast is going to go in the water a litle but the base should be a few feet in the air, so it doens't seem like it would need to be sealed at all. Then again i guess it couln't hurt as long as the mast can drain somewhere. how big of a drain hole is ideal?