The bondo putty patch on my Garelli gas tank failed after 4 years and now leaks. I patched it in San Diego whilst away from my tools. I'll put a spot of JB Weld on it after thoroughly douching the tank and we'll see how long that lasts. I don't want to ruin the paint with brazing. I am aware of epoxy putties made for car gas tanks but have never tried them. Success no doubt depends on the prep.