When typically "mufflers" are changed on the w124 300Es are they sold as a complete bolt on unit from the back of the cats all the way through what I think is first the resonator then through another pipe and then to the muffler. Or does it have to be cut and welded to the resonator? I have a some dry rot developing in the pipe between the resonator chamber and the muffler chamber what would be the best way to fix it. Thanks for the help