The simple rule is NEVER use screws in FG. They will always fail. Fastener
load must be distributed with some kind of backing.

That would make good sense if it were possible. The boat was built with no
backing, and there is no access to the inside now.
Any suggestions?

I could possibly move the thing the ropes from the jib go through out about
6 inches from the seat to the gunnels, where it can be bolted on. That
would take stress off the seat, but would change the geometry of the jib
somewhat.
Would that make sense, or would it ruin the boat?