German Automotive on Ascot drive are good. They fixed the old clicking dash board fault for just over £400, half dealer price. they have a couple of ex-merc mechanics there.
But...Benz main dealer in Derby will price match most jobs and for a brake fluid swap are cheaper than GA. Adam at the main dealer always sorts me out a good price and several times the car's gone in and had a STAR, no charge.
Come service time I got my oil from Costco and merc Derby were more than happy with that.
MOT at merc is £35 with a £500 insurance for MOT repairs thrown in.
Ring both places and compare prices first, i was surprised just how competative Merc are (...in Derby at least!)
And a main dealer stamp does look good in the service book...