Had a similar problem on a buddy's Tracker TX17 ... we temporarily fixed the leaks with Knead-it, and fixed some later leaks with JB Weld, but he eventually had them all welded (Aluminum welded) by a welder at his workplace. Rivets can also be removed and replaced.
I'm sure that if Flex Seal had been around back in those days we'd have probably tried using that, too.