My 5252 has the Kohler engine and is about 2 1/2 years old.  Last fall I noticed the muffler had developed cracks where the header enters the main muffler body.  The cracks appear to be in the metal and not in the welds.  I got the muffler replaced under warranty after some hassle with the dealer.  This weekend I noticed a change in sound of the engine and checked the muffler.  It again had cracks in the same place as the first one.  In addition there was a hole the size of a nickel near one of the cracks.  Almost like the metal is brittle.  Anyone else having this problem??  I'm out of warranty now and these mufflers run about $130, not that I would buy one.  I'll probably weld up my own this time.