I have three and none have shown any signs of melting. I am always conscious of them when using a flamed heat source, making sure the flames can’t come up the sides and touch it.
I have a weldless fitting that came with a silicone washer (wide and flat) instead of the little o-ring. It sticks out around the edge of the fitting completely exposed and it still hasn’t been damaged on my banjo burner.
My only problem with the gasket on the outside of a weldless bulkhead was trying to get a jump on heating my strike water up by lighting burner while getting the hose ready to fill the keggle With no water and a full tilt bayou burner the smell and smoke had me dropping the hose to kill the gas. Never did replace that little guy, looks a little crispy on the outside. Still no leaks.