Update: Today I dropped the mast and there was quite a bit of water inside. Of course I was in my wet/dry slip at the time (ref: my thread here: http://www.hobiecat.com/community/viewtopic.php?t=1037 ) so I couldn't really do much work on it aside from put silicone around all the rivets. My lower mast plug must be good because no water was coming out a little hole there (now plugged with silicone) but it did flow slowly out the top of the mast once it was dropped. HOLY COW a mast with water in it is heavy and difficult to lower and raise!

Next weekend I plan to pull the boat out of the water, drop the mast, drill out the rivets on the top of the mast, remove it, maybe put in a new upper mast plug, and then re-seal the whole thing. Hopefully that'll solve the issue. Any suggestions y'all might have are very welcome! I really don't want a mast bob because I think they look silly. 'Course not as silly as a turtle, but still...