Best product for sealing chainplates??
Your basic problem is that you want to know the best bandaid to use when in reality your looking at a chainplate/seal/seal cover ''system''. The best alternative you probably have, assuming you have typically small/flat deck plates with slots cut thru which the chainplates pass AND you only want to regoop at the deck edge and screw the plates back down, is to replace the plates with ones that incorporate an indentation on their underside, allowing you to amass a larger body of goop and get a better encompassing seal. (Forespar or someone else in the rigging business sell these, I was recently told). The less desireable choice is to ream out the old goop where you can, clean up the back side of the plate, and then reseal/refasten. Bedding compatibility, sealing in of moisture, and especially the inability to get fresh goop into the seams where the chain plate passes close aboard the slot cut in the deck are problems with this approach, tho'' in truth this is what''s commonly done. This is also why people are finding they must redo this frequently (after they once again find deck leaks at their chainplates) and why deck coring is ultimately found to have failed due to water penetration.
If the offseason allows it, why not pull each chainplate? You''ll purchase peace of mind for starters, and get the job done right for an extended period of service. You''ll be able to do a proper coring repair or epoxy sealing, bevel the slots to hold far more goop, and then fully rebed with a single flexible/high density compound like 5200.
If some chainplates are easier to do than others, do the easy ones and see what you think of what you found, and how easy/hard the job is. That might provide further motivation.