yes , it will leak just sitting in the water. no, I'm not worried at all about the rubber, the muffler is filled with water and keeps it cool normally. if it was a heat issue i dont think the muffler would be made of fiberglass. there are some small rubberish pads in spots under it already, if there still there, but there in the wrong place. mine was missing one completely and the other one was barely holding on. I'm sure the adhesive wore off long ago