Kind of curious about this, too. Mine doesn't leak much, but having it well-sealed would be good peace of mind. I'm guessing just some marine silicone around all the fittings to the mast (pulley on top, foot on bottom, and all miscellaneous rivets).
My other problem is the number of rivets that have been replaced over the years have left my mast sounding like one of those rain sticks when I raise or lower it. They all rattle their way in there to the top or bottom. Haven't cared enough to tear something apart and remove them, though.
1983 Hobie 16 "Rumpshaker"