deck leak

Are they straight screwed in or machine screwed with nuts, which would be inaccessible with the fiberglass inner shell? i’ve got some deck flex that I think is due to possibly these. having said that though the deck on top of the cabin is the area with the least if none deck flex on the boat...

Greetings, I have a 1981 Ericson 28+ that has developed an annoying leak from the sheet block track that finds its way onto the counter top in the galley. I wondered if anyone has ever used this stuff called Gluvit? They claim it will seal leaks and remain flexible to keep it sealed...