Check you local auto parts store, form-a-gasket by permatex comes in several different colors mostly blue and black with some clear,red,orange and possibly yellow.And the color usually depends on its use and heat range. I use the standard blue for Valve covers and water pumps on my motors. put on a bead,let it set up for a while,then it should seal fine.don't know about silicone and epoxy or varnish compatibility though. I would also put it on the hatch so when you have them off the boat the odd color wouldn't detract from the beauty of the boat.Also check the package fo compatibility they usually list what materials the specific sealant works with. There are a lot of choices certianly one would work.Try saran wrap for a release agent.make sure it sets up fully bfore removal.Sounds like the man didnt wait long enough.