Not that far away from MK/Bk'ham, there is Diagnostic Services in Leighton Buzzard, they always seem to sort out any problems I have and take a keen interest too. Lots of garages now must be so used to plug in and diagnose with software, that an older car is a challenge of real skill!. A bit further away there is a garage in Chesham that Rusty's uncle told me that he uses.
Your original post was a while ago, hope you've got it sorted, but there are places out there!
Chris