Deckhead repair

[Brion Toss]

Hello,
Many of our clients face similar problems, especially with older boats. In addition to the above suggestions, you might want to check out a recent issue of "Professional Boatbuilder", which deals with this subject in novel ways. Then contact the WEST System people, for free info on these repairs.
I think it's best to have something more crushproof than plywood under a mast, like solid "glass" or epoxy. If the mush is really extensive, transition to core further out, lest you make the boat too top heavy. And check around any conceivable water entry points for similar damage; the birdbath around you mast might just be a canary in the coal mine, if you'll pardon the mixed metaphor.
Fair leads,
Brion Toss