Are you talking about the little piece between the cylinder and muffler? I've had one break too. While more expensive than a replacement stack is, I highly recommend replacing the entire muffler assembly with a [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXZ653&P=SM]Macs Muffler[/link]. It's one piece, a heck of a lot lighter in weight, and really wakes the engine up. I found my GS-40's perform like an entirely different engine the Macs muffler and a MAS 10X6 prop (they don't like the APC or Xoar props for some reason).

I won't run a stock muffler on my GS-40's any more, only the Macs muffler and feel it's worth every penny Tower charges (I tend to run Macs mufflers on all my 2-stroke engines now).

Hogflyer