John Forbes wrote:
If you have a full alloy mast (no Comptip) then there should be two seals. One about 4-6” down from the top. The top one has a foam plug held in place with silicone and an alloy plate to hold it in place. You can see and feel this if you pop the mast head casting off.
The lower one should be just above the rotator/diamond wire bolt. Again, it is a foam plug held in with silicone. It can be seen if you pop the mast base casting off.
Interesting. I knew about the lower foam plug, but not the upper one. I wonder if they deteriorate over time, because it seemed to me that when my mast had water in it, the water was able to run the entire length of the mast. Once I stepped the mast and left it up for a couple of days, the water was visibly draining out the mast rotator holes (very slow trickle), and seemed to have drained completely after that.
Good advice on the corrosion. Fortunately for me I sail only in freshwater, so it's never been an issue on my boat.