I had a similar issue a few years back. Sanded that mast portion down to shiny aluminum
and put on a few coats of automotive primer and covered by 3 coats of epoxy paint
, both $4-5 cans from Walmart. My boatbuilder
buddy traced the issue to my wet bilge (that's my next project
, either restuffing or replacing the stuffing box) and interaction between the ss keel bolts
of which I have 11, and the mast and the step (which is also aluminum and probably ready to be replaced soon). Since then I keep a bunch of old zincs in the bilge taken from the old zincs pale at the boat yard and the problem seems to be contained as I check that area often.
This is one of the few deficiencies I find with the builder/designer of an otherwise fine boat. I may even replace the existing alum mast step with G-10 box epoxied in, if I get handy enough to DIY. On the other hand a local rigger at the boat show
quoted a few hundred bucks for the new aluminum step plus may be as much for the installation
. And if it'll last another 35 years it just may be the most reasonable solution.