The original system on my 300SD lasted 19 years. (That is pretty good don't you think?) At the time I didn't know about Phil at Fastlane or I would have bought a Stock system. Performance has about the same prices as Phil But they gave me some kind if razamatazz about how exhaust pipes couldn't be shipped by UPS and that shipping and handling would be a couple of hundred bucks.
My experience with muffler shops is that you have to go back every 2 years because they use thin pipe that they can bend easily. They give you a lifetime warranty on the muffler which rots out in about 2 years and when you go back to get your free muffler system you find out that the the muffler is free but the pipes (which are also bad) and the labor to install them is extra. After the second trip back you always wish you would have done it right.
Vowing never to get caught in the Midas trap again I bought a complete Timevalve stainless steel system for $700 shipping and all. That was for headpipe, front and rear mufflers, hangers, gaskets and UPS shipping.
http://www.timevalve.com/cat/us/p15b.html
It took about an hour to install in my garage.