i recently acquired a 35 year old aluminum canoe that has a couple VERY minor leaks at the rivets. how hard is it to replace the rivets? also, the marina where i got the sticker for it today tried to sell me this "stuff" that comes in two tubes that you mix together that will supposedly seal the leaks and is permanent. apparently you can sand it, drill through it, and even tap threads into it once its dried. any suggestions?