Slow leak from transom... goes blub blub

Well, I finally got the stereo in the 84 SN2001. With that, I added a second battery, cut a hole in the back wall to make room for the battery and now I see a leak. I think it's coming from the speedos, exhausts, or where the platform is bolted in. I don't want to take it out of the water... I can't see under the fuel tank what the inside structure of the boat and exhaust tubes look like.

Assuming I do take it out of the water and see a loose screw or...? How should I fill it?

I would take the screw out, then mix some epoxy resin with chopped up fiberglass cloth.

Using a nail or something similar, push the 'mash' into the hole. When it hardens, you can redrill it to the correct size.

Even better is to remove fuel tank & do a repair from inside.

not difficult.
have to remove the fill tube vent tube and sending unit wires then unscrew the mounting screws on each side of the tank and pull it out.