The most effective way to seal the rivets would be with brass or silver solder, but that's also the most labor-intensive method. Given all the stresses a wheel undergoes during normal driving- - - -potholes, steering inputs, washboard bumps, etc., I'm not sure any of the recommended procedures such as epoxy paint, powder coating, and such would seal a slightly loose rivet for very long, if at all. Most riveted wheels hold air pressure well without doing anything heroic to seal them. A riveted wheel with an air leak should probably be replaced anyway.
Jerry
