Hi Dave, thanks for the tip. I've a drain tube as well. The leak developed on the portside bottom of my tube. I could not tell if there was a hole or if there was a failure in the tape/step join.
My solution was a bit different than yours. I cut a 3 5/8" (should have been 3 3/4" for a better fit) hole in a piece of 6mm ply and then made a collar for the base of the mast tube. Slathered it with epoxy all around, put a coat of thickened epoxy on the bottom and fitted it to the base of the mast tube where the leak was. I put a generous fillet around the collar and tube and then laid a few pieces of fiberglass tape soaked in epoxy on the collar and tube. I was doing this blind as my arm was about the only thing that could fit in the opening. Woodenboat would not be pleased with the subsequent mess, so don't expect a pretty photo essay in that esteemed magazine, but I think it will do the trick. I'll know tomorrow a.m.
BTW, I loved the video of your boat you posted sometime back. It looks like you had a great sail that day.
Best,
Traddles