If you use Sillycone you'll have to live with the consequences which aren't pleasant.
Use a Polyurethane
or Polysulfide caulk. Believe Westsail used Dolphinite to bed
the cap rails. Unfortunately that dries out over time and stops sealing. The hull to deck
bond was either a polysulfide or polyurethane sealant
which works well but unfortunately they pierced the joint with hundreds of sheet metal screws with poor caulking to install the cap rail. Pulling the caprail and rebidding with Butyl paying special attention to the fasteners would probably solve your leaking issues. Problem would be pulling the plugs for the fasteners without making a mess of the wood unless you'd also be replacing the caprail. Think Westsail used glue to set the bungs which makes removal
an issue. Might try and pull a few of the plugs to see if you can get them out without damaging the surrounding wood.
Trying to seal the caprail/deck line without pulling the caprail is almost guaranteed to fail in short order. Have tried that out of desperation on several different boats and the caulk seal failed rather quickly probably because of the different expansion characteristics of wood and FRP and the poor adhesion to the wood.
Had a friend who built an early Westsail kit and glassed in the hull to deck joint. It worked great but looked pretty sterile. The teak
cap rails that are normal on a Westsail look way better but have to be installed with care to seal the fasteners. On my current boat
pulled the caprail and glassed the hull to deck joint. Hired it done which was costly but the results were excellent. Carefully caulked all the bolts reinstalling the cap rail so no leaks
from them or anywhere on the caprail anymore.