[rotorwrench]

Originally, Ford used a process referred to as terne plating for the whole inside of the tank to seal it. This is a lot like coating the inside with lead/tin solder. A lot depends on the condition of the joint between the bracket and the tank. They have a reinforcement plate on the inside which was all riveted together with the tank & bracket. They tend to crack after many years of use and abuse. A person can try soldering it up but it's too easy to have contamination come through to the outside during the heating process. It will have to be super clean to get it to stick. If the tank is rusty inside then a solder job on the outside may not last very long before it starts to seep again. If the tank skin is cracked then it won't last long at all.

Major work on a tank requires cutting it open on the original seem line and performing complete cleaning and repair before welding it all back together and sealing it up. It's not an easy job. It's getting harder to find good clean and serviceable tanks these days but they are out there.