If you have actually seen the muffler disassembled (doesn't sound like you have) you would see why soot wouldn't just accumulate at the flange. I stated earlier the exhaust pipe extends beyond the flange slightly inside the rear muffler (the exhaust pipe is slightly smaller then the opening). No, soot would not readily be accumulating on the flange.
Except that you can clearly see that the soot deposits extend right to the point where the edge of the gasket would mate. This shows that the muffler pipe and exhaust pipe did not create a "slip fit seal" with the smaller diameter exhaust pipe slipping inside the muffler pipe. Therefore the scenario as you explained it is not plausible.
I never said the original muffler assembly was leaking, but that simply that no gasket was installed. The part was missing it's as simple as that. No need to even assume someone is trying to lie about it, or that they were careless. Mess ups happen whether it's made by hand or machine.
Your right about that. In fact, cars assembled in Japan by Japanese workers are notorious for being delivered with missing or damaged parts. For example, my CX-5 was delivered without the following parts:
1) One of the two nuts that holds the tailgate latch on
2) Two doors (left side) each had one of the hinge mounting bolts missing.
3) The nut that tightens the positive battery clamp.
4) The left rubber driveshaft dust boot on the rear axle.
5) The center exhaust pipe hanger was missing.
6) One of the bolts that holds the rear differential halves together was left off.
7) Left rear wheel was missing a lug nut.
8) Passenger side sun visor was missing.
9) A missing screw on the glove box assembly.
10) No lug nut wrench in the spare tire area.
So, as you can see, I am very aware that humans can make mistakes (especially those low paid Japanese auto assemblers who don't really care).(wink) But in your case the evidence shows they miraculously managed to correctly assemble the exhaust flange but the gasket unfortunately fell out at a later time when no one was looking. That's what the photo shows.
However I don't see how anyone could believe that an auto manufacturer can't make mistakes during assembly.
But I do believe a manufacturer can make a mistake during assembly. Just look at all the parts my car was missing.(wink)
It's a good thing I did a thorough inspection before I took delivery - otherwise I would have had to replace all those parts out of my own pocket.
