Did you store your boat mast up for the season? Did it rain? What happened to me (assumed, since I could not actually see this) was that the two piece mast creates a cup for water to collect in lower section above the foam plug and it crept in around the plug.
Pull the two mast pieces apart and look into the lower mast. About 6 inches in is a foam plug. The standing water and age can degrade that foam and allow water into the lower section. Heating and cooling cycles of summer weather can expand and contract the air in the lower mast volume, "pumping" the standing water through the aged foam. My lower mast was completely full of water, to the top! My foam plug was so bad the water poured out when I lowered the mast (dropped, since it weighed 100 pounds!).
The plug is readily available and cheap. If yours looks ugly you might just pry it out, pour out the water, and replace it. Or you could just drill a hole through the foam plug, drain the water, and then plug the drain hole with some silicone caulk.
I've heard of people putting a tire valve in the mast base and removing the Schrader valve core to drain the water. Seems silly. Some idiot would pump up the mast with air, swearing he sails faster with 80 psi on board....until the foam plug blows out, shooting his upper mast section 30 feet in the air.
