Mat,

              Looks like it got very warm in there!  The middle tube is starting destruct, nothing you don’t know.  I tried many systems but failed to keep the noise down.  Hence the turbo and a muffler as well.  Yet to be tried.  The muffler is a straight through with packing.  15LBS is the problem and now putting it out in the airstream. 

Mat I would suggest a slip coupling at the end of the muffler where it broke, and dish the outer and inner of the flange to allow flex where you have welded the end in the muffler.  Make the flange bigger and heat to form a 3/8 the both flanges. I used a small hammer to make the dish on both inner and outer.   It does make welding the “filler” flange easy with the flanges on outer and inner.

Regards,