One thing I learned from my friend, an MB trained mechanic who ran his own shop locally for 20 years (just retired), and did virtually all the foreign cars in the city, was that the aftermarkets never sound 'correct'. They might fit OK, but there is a lot of internal baffling and whatnot that Mercedes engineers into their exhaust components, which are designed to work together. If you must use aftermarket, try and at least keep the muffler OEM, or be prepared for a nasty surprise when the car no longer sounds like a Mercedes should.

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1986 560SL
2002 Toyota Camry
1993 Lexus