Turn the barrels upside down, heat the top (now on the bottom)rib with a oxy-acet torch until it falls off. Clean/sand, tin with acid flux, clean with a base (soap, baking soda, etc) using some type of method like Scotchbrite to ensure all the acid residue is gone, then use rosin flux for the joining. Wire it back together per standard method, heat until fused with a fillet all along both ribs.