Ernest,
 
Copy you on that!  What material type and thickness was the Mistral muffler?  Anyone know what their design was like?  I know that something fatigued and plugged the flow, but I never saw a drawing of their muffler or had anyone explain how the failure actually occurred.  It could have been a baffle plate that was not well supported on all sides.  I don't see how that could happen to my muffler as the tube is welded to both end plates and the exhaust gasses don't strike the tube directly but swirl around it.  Yes, a piece may fatigue over time and crack off, but I can't imagine how it could plug up the exhaust path.  But I guess anything is possible if Murphy has his way.  I'll keep a close eye on it though.  With a little finessing, I'm pretty sure I can get my little inspection camera up the tailpipe.  If that fails, I can remove one of the O2 sensors and stick the camera through the hole for a peek inside. 
 
Mark 
 
Here is one version of the Mistral muffler. Said to be the failed version. Well thought out. Superb exicution. Note that there appears to be a slip join in the main body between the flanges.  The whole muffler is encased in a cooling sleeve with a big blast tube on one end and a coaxial exhaust areounf the down pipe.
 
My vote for the failure point is the flat disc closing the end of the perf tube.
 
Nothing flat survives the pounding. If its flat it dies. Round, conical or spherical, yes. Flat no.
 
Lynn E. Hanover