You may never be able to stop chainplate leaks forever but you can reduce or eliminate the problems related to leaking chainplates. The first thing to do is to protect the deck coring by picking out some and filling it in with an epoxy filler. Then protect the bulkhead with epoxy in the bolt holes and varnish on the surface.
There's lots of speculation as to which sealant is best for sealing the chainplate at the deck. I used 3M 5200 in and around the hole. Then I lightly pressed the chainplate covers down on the sealant. After the sealant cured, I screwed the plates down tight to compress the seal. Seems to have worked just fine (2 years now).
Good Luck.
