Dear Caleb,
I redid our 1967 chain plates 4 years ago. There was no sign of a problem rxternally, but drilling a small hole brought out moist pulp on the bit.
When I opened them up (p + s) the bolts (galvanized) were rusted almost completely through. I don't think filling with epoxy would have done nearly enough to strengthen the plates connection to the boat..
Long story short: I replaced the knee with epoxy encased marine plywood, and then used longer ss bolts so the heads and nuts are on the outside of the fiberglass.
Good luck with your project!
A marine surveyor told me to drill some holes in the knee wall of the
port and stbd chainplate support structures and let it dry and fill it
with epoxy starting at the lowest hole first. You put duct tape over
each hole as it is filled from above and the whole structure should be
more seaworthy. I have only drilled some drainage holes on our T27
chainplate knee walls and have not tried to fill them with epoxy yet.
