How to fix a leaky gas tank by soldering it. Fixes, pinholes, small cracks, and seams without painting. Easy Step by step. you can do this, because a leaky gas tank sucks, stinks, is dangerous. Remember " Vintage motorcyclist is a person willing to take a container of highly flammable liquid, place it on top if a old hot running engine that has the tendency to pop, miss and backfire, and the put the whole lot between their legs and drive down the road a high rate of speed.