It doesn't directly help on your question, but this may help, anyway.

I have not had a problem with mine since I got rid of the (ridiculously) expensive stock muffler, and replaced it with an $18 generic-type, and a standard, off-the-shelf 90� elbow.
I just made an adapter to standard 2" exhaust pipe by welding together a dead converter flange and a short piece of 2"pipe. I installed this adapter on the end of the converter, in place of the muffler. Now I can clamp any muffler I want on the end of my adapter, and with 2" in and out of the muffler, I think it breathes better (especially on  the H-way, at higher RPM.)
I think it has all the good things about back-yard engineering
CHEAP
CUSTOMIZABLE
CHEAP
EASY (If you have access to a welder set-up)
CHEAP

Did I mention CHEAP....?

Evan Mac Donald

1984 Wolfburg
1985 GL 7 Pass.
1991 Carat Weekender