Leak in fuel tank

The fuel tank has two fuel taps, one on either side. Unfortunately there are leaks around both of them. Last time I tried to just fill them with some epoxy putty. Unfortunately that didn't work. Now that I am waiting for the spare part for the engine I am trying to fix the leaks for good. I first cleaned up the putty. In the photo below you can just about see the hair crack. I will solder the cracks and hope that works. I will not paint the tank before I have used the bike again for a while to ensure the fix really works.