Hey mr bill- It sounds like somebody "re-bedded" the seal for the hull/deck seam.
It originally was sealed with clear silicone and fastened with aluminium rivits. (My 2 boats anyway) I've been tempted to do the same in the past to make a mold. Never got that into it. I'm paddling around some open water I found on Lk. Champlain this week. 1st time out since Jan. duckhunting, east end Long Island, N.Y..
All the best- Bilnik