I would suggest what you and a previous poster mentioned, redoing all the stanchions and any other deck fittings that are through bolted through the deck first.
- - Messing with the toe rail and its huge number of bolts is a very last step. One thing that can be done. If the bolts shown in the diagram in post #3 have heads or heads with a little bit of an edge - try to get a vise-grip pliers on the head
and gently see of the bolt can be rotated. If so then probably the sealant is not longer attached to the bolt shank and water
will pass down the shank of the bolt. Any suspect bolts can be replaced individually without having to replace all the bolts.
- - If that is not practical then surgically and chemically clean the bolt head
and surrounding toe rail area and apply a good UV resistant adhesive
sealant over the bolt head. That is assuming you don't really want to get into a major reconstruction of the deck edge and toe-rail.
- - If you can, using water, possibly colored - try to determine if there are gaps in the butyl rubber between the toe rail and the cabin top. If so, you can carefully grind a furrow down the inside of the toe rail into the cabin top a little bit and after cleaning
well - lay a bead of adhesive
sealant down that edge of the toe rail.
- - If the leak does not seem to be from the cabin top down then you are left with the joint with butyl tape between the FRG cabin top and the Hull flange. Here you would have to use a strong stream of water pointed up at the toe rail "overhang" to hull joint. This is where ocean waves lapping up the side of the hull could enter underneath the toe-rail and migrate through the cabin top to hull flange joint. Again a shallow groove, cleaned and then lay in a bead of strong adhesive sealant.
- - All of this is rather time and labor consuming and a lot of work. So investigate all the other possible areas where leaks could be such as "spider cracks," crushed FRG due to a repaired collision
damage; deck fills; etc. The most common source of leaks is dried out sealant not sticking to the metal bolts anymore or broken free due to hull flexing.