I've used JB Weld to fix a hole in the crankcase of a 250cc Motocross bike - it would hold up for about 2 years at a time, then need to be replaced. I also used JB Weld to fix a pinhole leak in the bottom of a gas tank. Emptied the tank, cleaned the area around the hole, slathered on JB Weld, pushed a small piece of sheet aluminum (about 1" X 1") into the JB Weld so that it went up against the tank. I then waited for the JB Weld to cure, and slathered more JB Weld on top of and around the aluminum. That lasted until the car was scrapped, about 5 years later. Probably not the best way to fix a tank, but it worked!