Actually there was a discussion on one of the other BB''s about a Tayana with this same problem. This boat actually had a deck failure in heavy weather with the deck actually tearing I believe near the edge of the cabin. In the case cited the fastenings for the deck were in a reasonably straight
line and the core had rotted out at each fastening. This created a weakened
line that buckled in heavy weather. When the teak decks were removed a large portion of the deck area was found to have rotten coring. The poster was trying to decide how to make the repairs, i.e. replace an entire deck.
Obviously, that is an extreme case, but I have always felt that there is no good way to install a teak deck over a fiberglass deck. No matter what the core material, sooner or later the fastenings will leak and water will be trapped and cause rot.
Then there is this hogwash that the rot can''t spread if small blocks of coring is used. Almost all balsa cored decks use small blocks of coring but the water still spreads and the rot still migrates. To prevent that from happening, the blocks would need to be vacuum bagged in, one at a time, using
epoxy or vinylester resin to saturate all sides of the blocks. That never happens.
If it were me I would run not walk the other way on this boat. Tayanas are nice boats but if the owner has allowed the boat to sit with 60% of the bungs missing this is a boat that will need a lot of help.
Jeff