If there is a 1/8" gap between the tab mounting plate and your transom...you are screwed! I would definitely pull those puppies off and let the transom dry out over the winter. Then install larger diameter screws with 5200. That is, if they will fit through the mounting plate.

I would let it dry out all winter first and then consider putting some penetrating epoxy like git rot in the holes. then do every thing stated above.
Unless of course you have very bad water damage, which would require
someone competent in doing that kind of repair.