You know I have used JB weld to fix a leaking tank once. It has been 6 years since I repaired it by rough sanding down to the bare steel at the leak and globing it on. My friend bought the bike from me 2 years after the repair and it is still keeping fuel in the tank just fine.

I know its hillbilly but it worked all the same. What do you have to lose? unless the leak is somewhere JB weld wouldnt work so well.