Both my Cavalier 32 (10m NZ sloop)
mast and boom are bare alloy. The boom was painted and the paint in bad condition when I bought the
boat 3 years ago. I had it sandblasted and then I immediately painted it with a 2-part clear penetrating (thin)
epoxy; just one coat as a sealer. I have not had any issue with staining on the
mainsail cloth, but I always put the sail gaskets between the sail and the boom, not around the boom, so the sail isn’t squashed onto the boom.
Surface
corrosion on proper
marine alloy is not a structural problem; just think about all those unpainted alloy French hulls.