Well I called the dealer and asked about the cost of a replacement cat .. The local dealer (RBM) wanted almost 1600 dollars for a replacement saying that the cat itself is 1350 dollars. My old dealer (park place in Dallas) would sell it for 800 and something. I don't care how much better a Mercedes Cat is I am not paying 1500 for a catalytic converter. I took it to the muffler shop recomended by a trusted tech and they looked at the cats. It appears that the factory front cat fell apart and blew into the back cat and hence rattled all over the place. He replaced both cats with high output cats (small and designed for cars up to 6 litres).

Total cost for replacing 2 cats is $450. If it lasts three years it would take me 9 years to break even.

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With best regards

Al