John - Yes I can say by just the picture of your boat in your signature it looks exactly like mine. I am thinking along the same lines as you right now by trying to seal the leak in the boat and then once the water warms up a bit diving under and applying something on the underside. I am curious and tempted to try drilling a small hole into that platform that the muffler is screwed onto just to see what happens - if it is solid or hollow and if water comes out. What do you think? Dumb idea?