As I said, pt, my GUESS is that the nut was damaged, and simply failed, rather than 'coming off'.

As for the black color of the exhaust, I considered that was well...and as old as that motor is, could well be aluminum. I don't THINK it was however...I think i was just getting so much MORE exhaust than normal, AND catching it more directly onto the plane...

In either case, the new OS will be installed tomorrow. I MAY go ahead and purchase another muffler for this one, and pass it on with my old telemaster to a buddy who's buying a radio this weekend.