Stumbled across your post - not my area but one of the MB forum members asked this question a while ago and ended up going to MB Centre in Nottingham, he said they're east of Nottingham so fairly accessible from Lincoln, and spoke highly of them.

Depending on the nature of the fault, whoever you go to probably needs to have the MB system, StarDiagnose.

I can recommend Mercserve in Nottingham.

I had a tickover problem with my C Class and my local garage was not able to cure it despite replacing loads of bits, at my expense!

Mercserve was able to diagnose it over the phone as a cracked air pipe.

Quick trip there and £120 later, all fixed!!

Address is

Unit 1 Universal Engineering
Radford Road
New Basford
Nottingham
Nottinghamshire
NG7 7NQ

mercserve.co.uk