Ours would take on water, too, which made it a little harder for lighter kids to right the boat after a capsize.
I took off the upper and lower mast caps by pushing in the litle pins that hold them in place (with a small punch and hammer) and then carefully working/prying them off. Then removed the ancient, dried up/rotted cork plugs at either end. Manually brushed/sanded corrosion out of the ends and sealed some corrosion pinholes w/ epoxy. Cleaned the end caps and placed a small bead of silicone sealant around the lip/corner where the caps seat against the mast ends, and then reinstalled end caps. Pins were replaced with silicone sealant as well.
So far, the mast has remained dry and waterproff since this treatment. Similar procedure for the spars (removed and reinstalled block straps with sealant on the lower spar).
Oh, also drilled and tapped the base cap on mast as a drain hole, then installed a short stainless steel screw with a rubber washer under the head as a plug -- just in case water works it's way back in there some day.
Neat idea. Make sure though that the screw is recessed (doesn't stick out).
In the grand scheme of things, a well sealed mast is the goal. If you detect a broken seal and water has snuck in, draining is just half the job, you still need to dry and reseal, rinse, dry and reseal in the case of salt water.... also drilled and tapped the base cap on mast as a drain hole, then installed a short stainless steel screw with a rubber washer under the head as a plug -- just in case water works it's way back in there some day.
I think you have the right idea and have recognized the drawbacks. Keeping watertight is the real key. Someone sailing saltwater would need to consider how to rinse.I used a pretty big screw (maybe half-inch diameter shank) so my drain hole would be big enough to drain water w/out too much trouble. Will probably leave screw plug out over winter to "air out" the mast interior (although doubt a hole that small will let much air circulate). So far the whole set-up has remained water-tight, though, so may not be a concern.
what if you opened the leaking end cap, dried the interior and filled it with that expandible form used to fill gaps when installing new house windows?
Then reinstall the end cap with good caulk.
then if something leaks again, the mast won't fill up.
Mike