The mast boot was leaking, but there was some tape on board. We removed the canvas cover and found some corrosion of the aluminum where the paint had been scratched. I cleaned this up using a wire brush on a dremel tool, and then touched up the bare metal with zinc chromate primer. Should be good until we pull the mast in the spring.
In addition to getting wet inside, the leaky mat boot damaged the headliner. Although it looked ok from the outside, the inside was full of mold and decaying plywood. PVC foam board was used as a replacement.The old headliners served as templates for the new ones.
Of course we have to redo the varnish and replace the rusty 18-8 SS crews with 316 SS.