I highly recommend a specialty Mercedes mechanic here in the city (San Francisco) called "Octane". This shop is terrific, they have an excellent facility, great staff, and understood where I was coming from. When I brought the car in I told them that I only needed them to diagnose the problem then I would work on it myself. One of the techs there knows the 400E inside and out and went through the car, checked all the systems and found out that it only needed new rotors, since it was an easy fix they installed them without any extra charged and got them for a good price. I would highly recommend them, they had older models (123's) as well as newer models (272's) in the shop.

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1992 Mercedes-Benz 400E
2002 Mercedes-Benz ML500