hi Joan, is the seat glued to the foam which is glued to the hull? How about just cutting the foam, removing the seat, then shredding the foam with a surform or nylon or wire brush attachment to drill and then lightly sanding the rest with a nylon scrub pad. Not sure if acetone will work on cured silicone but would probably loosen up some contact cement. The acetone shouldn't harm the fiberglass on the inside,on the outside colored gel coat it might make a little color come off with hard rubbing but that's about all. What does Ian say?