I'll try again,

Any suggestions on how to remove a good dose of waterproofing (non
silicon) from a fiberglass and resin (vinyl Ester) lay-up?

Can it be done safely and with no lasting, or long term aftereffects?
This is inside the horizontal stab where strength is pretty important.

I'm to the point of installing the hinges, or pitching it and starting
over if I can't clean it to the point where I'm satisfied future bonds
will be secure under high stress.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com