The best fix is going to be to pull the carbs so you can get at it , get some Loctite sleeve retainer, coat the fitting with it and drive the fitting back into the case solidly with a brass punch or a drift, you need a good straight shot at it to do this which is why I say remove the carbs, let the Loctite cure , reinstall the hose and go ride. Red loctite would also work but sleeve retainer is a more permanent fix.