During my time in MB I had good experiences.
CL600 bought second hand through their network and a number of large jobs needed doing. Never had to question it.
E63 estate has only a couple of minor niggles but they got done without a question.
I am in the middle of a terrible saga with Audi (where the dealer has done a good job in truth) with some wobbly wheels that went off centre.
It does seem to be a bit of pot luck with the dealer, car, error and approach.
