I recently repaired a pinhole leak on my 41 Chev by soldering it. The hole was near the outlet where the original soldering had started to leak. I do a lot of soldering in my daily work, so I was reasonably well- prepared. I used pure solder (without internal flux) and a mild plumbers flux from a tube. I took special care to clean the area around the leak to bare metal or to bare old solder. I could choose one of our normal larger soldering irons with good temperature control. If one heats up the flux or the area too quickly it becomes dirty or oxidizes again and the solder does not attach well.
Without the proper tools and some patience and experience I would not recommend this method. If you lack experience, make sure to find some old rotten tank to practice on first. Be sure to have the right iron and some kind of thermal control.
Karl
