In most edges it is molded to the underlying deck, but in a couple of areas it wasn't epoxied properly to the underlying deck, and that is where it has started to leak.

Sounds like folks are leaning away from butyl rubber, so I might try DDW's idea of a flexible tube to extend the reach of a caulking gun so I can use Sikaflex. Otherwise I'll look for a different sealer that is available in a small tube. I had put BoatLife (or similar) in there before, which eventually crazed and cracked, which is why I want to get the best possible sealer in there this time.

Thanks for the responses.