Just a wild guess.

The water is coming into the mast through the T-terminals slots just below the hound fitting. Very early on it was recognized that these slots could never be made fully watertight and that a better (cheaper and quicker) alternative was to just pop rivet SS endplates to the mast (these CAN be made watertight). Of course some people just knew better.

From experience I know for certain that when the boat capsizes that the diamond wire end fittings WILL go below the watersurface. Not for all time but definately long enough to let water in. Most likely situation in this is when you are still hooked on after the capsize or when standing on the boom to free your leg of something. The boat will not turtle because of this but it will put the diamond wire end fittings under.

My mainbeam was made from a old Taipan mast section and the amound of sealant around a T-terminal opening suggested that this issue was already discovered on the Taipans well before the F16's were build in larger numbers. At least I knew this when I builded up my mast several years ago, so others must have known as well.

Wouter