For what it's worth, my experience with mufflers has been that so-called "overhaul shops" will essentially build you a new one for a price far less than one from Cessna when you send them the old one. Regardless of the condition of the old one, even if it's in pieces, nothing but junk. Essentially, they use one or two good parts of the old ones -- like the clamps! -- and build a new one around those parts. They call it "a repair". Yeah, like they replaced 99% of the item. But it's worked for me.
Next time you need a muffler, call some of the muffler/exhaust shops with display ads in Trade-A-Plane. Tell them what you've got and what you need. You might be pleasantly surprised.
For new participants to this forum, this and other tips that can save you big bucks in repairs can be found in the "purchasing Parts" page of my backup website
www.SkymasterUS.com
Ernie