That's the thing Gazjen, the rod will melt in the flame every time but crumbles and doesn't weld. This type of rod brazes by melting into the metal,to get a good weld the metal is first cleaned with a stainless steel brush and then tinned, the metal is cleaned again through the tinning and the brazing commences. Aluminium melts at 600c and any item being worked on only needs to reach 400c for the rod to melt.
As you say it may be that the thinness of the lip is dissipating heat to the rest of the casting, or to the air. I have also tried to heat from the other direction to push heat through, that didn't work either.
I'm wondering if there is a high Magnesium content, Brunswick didn't mention it. I have noticed that the ring on which the bellows sits, seems to have a weld connecting it to the main bell housing, I'm now wondering if it is impossible to repair this item.
Ed, I may have to take you up on your offer.