Ouch, sounds like a hand full. I believe your blade is a VMI blade correct? When I got mine, the top mast plug was one of things I changed after a few sails. Reason was, I capsized a few times and the mast went further down than what I was comfortable with, so I assumed the top plug was leaking.

On my blade, there was a loosely fitting blue foam plug, under what seems like another silicone or 4200rtv plug/cap. I removed all this stuff, the foam was already soaked in water. I replaced it with higher density foam and the foam was cut bigger than the mast. Because it was cut bigger than the mast's profile, when I installed it, it was a huge pain in the butt task. But once it was in, it was in and NOT moving anywhere. Plugged it all up with silicone sealant and called it a day.

What I am saying the TOP MAST PLUG that comes stock with the VMI blades is not a very good one. You should change it.