[Yosemite Sam]

Yes, the little square fitting is soldered to the tank.

I have had good luck repairing leaks by re-soldering them.

It usually only takes a little heat and some flux to clean the existing solder well, several times I haven't even needed to add more solder (that is not the norm).

I always screw a long 1/8" pipe fitting into the square fitting to use as a handle, to prevent the fitting from falling into the tank once the solder liquifies. Lose one in the tank and they can be a bat turd to get back in place (trust me).

Sorry but I don't know how to fix one properly without messing your paint up.

Be careful with open flames and gas tanks...