Austin wrote;
>>Sadly) they WANT you to return for warranty replacement - often!!!  It's where they really make their money, because while the >>muffler is under a generous warranty, the LABOR is NOT!  You WILL pay, +pay,+ pay until you catch on.  Figure how I >>know.  Guess how many mufflers it took to figure it out. duh on me.

I do not think this is always the case.  A few years ago the muffler that came with the S&S header kit on our van developed a split.  (I'm not complaining, it had been on the van for five or six years).  We were traveling so I went to the nearest muffler shop (Midas) and they replaced the muffler with a similar unit from their stock.
This summer we were traveling again and I noticed that the tail pipe was a little loose, I went to another Midas shop and they fixed (welded) it in less than one hour (including waiting for the hoist to be free) for no charge.  I offered to show them the original bill but they said they did not need to see it.  
George 
'85 Westfalia