Prior to taking over the responsibility for a 64' IIA, my dad had someone take care of rust in the fuel tank. After putting some fuel in, I discovered a leak. The plug wasn't in the whole way and someone attempted to cure the problem with silicone. I removed the plug, cleaned the threads, and put the plug back in place, this time it seated properly. After an hour with a splash of fuel, it again was leaking.
The plug is actually an insert which fits into a whole leaving a raised ring in the bottom of the tank. There appears to be a break in the seal where the insert joins with the tank. I wiped it clean with a paper towel and can see gasoline weeping into a small crack on the inside of the ringed area. I can't say for sure, but I suspect it was originally soldered in place.
Are there any alternatives for repairing the tank? There are some obvious issues with welding it, and while the risk may be lower, I suspect soldering would be fairly dangerous as well.