I had a variation of the previous post. I lowered the mast, but forgot to re-attach the guy wires to the boat. The mast thrashed abound a little and broke the forward end of that fiberglass piece. The break took the form of a crack down each side of the fiberglass piece abeam of where the mast sits.
After fixing the cracks, I made what I think is not a bad idea to do proactively even if nothing is currently broken. The mast mounting base is originally just bolted to the fiberglass piece, which is in turn held down to the boat by some small wood screws along its lower edge. I unscrewed the forward end of the trim piece inside that has the lights, for access, and installed three 1/4-20 bolts Through the mast base, fiberglass piece and cabin top, with nuts and large washers inside. Much stronger, and will save breaking the fiberglass piece if you slip somehow while raising/lowering mast.
Larry