For most cases of a leaky rivet, you can tighten the rivet back up. Have a buddy hold a trailer hitch ball against the rivet inside the boat and give it a couple of solid hits with a hammer on the outside of the boat. This should swell the rivet into the hole and prevent further leakage. Note- Don't over-do it with the hammer. You could compound the problem if the rivet should split. Only a couple of hits should be needed.
As far as sealing a leak, the JB Weld could work as long as you get it well into the leak. It might also be prone to fail eventually as it's only a surface repair. There should be good/better sealants available at local marine suppliers.
As for paint, the preferred primer for aluminum would be zinc chromate. I'm not sure where you could get it, but in the USAF we used it in a spray can or 2 part mix. If you can't find it I would suggest asking your local marine dealer what they could recommend. Remember, use the best primer for the type of paint you'll be using.
Hope this will help.
Jesus still hangs out with fishermen.