Isnt there some Ex main-dealer guys on the Industrial estate on prospect lane , The only experience I have is that my fathers C250 was serviced there by its last keeper and MB parts and diagnostic processes/ checklists are seemingly followed. I think theres also a german focussed place on cranmore ind est as well?
I've not used either of them (yet), but have been passively looking for a good indie, so would be very interested to hear how you get on as I'm not too far away.