pepin, i haven't gotten my old 5.2 mast down yet so can't say what is happening but if you are having problems sealing your speader/mast join it is probably because the through bolt? is a smaller diameter than the hole for it in the mast and as the mast flexes the diamond wires move the spreader around with enough force to push out soft stuff like silicon sealant

you could make up some washers that fill that space and then epoxy them in. if you ever need to pull it apart you could use heat on the spreader bar, not the mast, to release the epoxy

but the spreader bar is pretty low down the mast and if that's underwater then the boat is already turtled isn't it?