Chris, I'd certainly recommend Zentrum - no need to schlep down the hateful M1 at all.
James at Zentrum cut his teeth on 944s in the early 90's at OPC Nott'm and I've been impressed by Zentrum's general honesty, efficiency and knowledge in the 2 years I've been using them. I only wish I'd used them since day one of 944 ownership.
If you're still unsure, do what I did when I first scoped Zentrum out - after several, shall we say, 'unsatisfactory' experiences with various specialists (including some named in this very thread!) - pop along on a Saturday morning and have a chat with them to discuss what you need doing. I did this and it immediately became clear that Mike and James know what they're doing and I was offered sensible and informed advice specific to my 944 and my long term plans with the car. My experiences with them ever since have backed up the initial positive feeling.
When I was last there a few months ago, James even mentioned there had been a notable spike in 944s coming through their workshop over the past 12 months. There's some further good feedback about them over on the TIPEC '
Praise or Grumble' section, which I suspect is the reason for some of the recent up-tick in their 944 business.
Next on the list for my 944 S2 is a pretty major set of jobs including the fitting of a new refurbed torque tube and a rear axle rebuild and rebush plus all new fuel lines. If I'm still living in south Nottingham this autumn then I'll be certainly giving Zentrum the nod to do all of this.
Zentrum even asked me on my first visit if I wanted my car cleaned or not as they are aware that many owners (of which I'm certainly one!) do not want someone else cleaning their car (my 944 still bears a couple of scars from another garages cleaning attempts!). They also said that if it was raining on the day of my appointment and I didn't want to drive my car in the wet (I don't!), then there was no problem about not coming in and they'd happily arrange another appointment. It's little things like these that reflect well on such local specialists - they understand the, shall we say, foibles of enthusiast owners.
If it's of any use to you, I can also recommend a good garage in Worksop run by guys who know their 944s. They did my belts and rollers last time and got that job spot on (unlike another 'specialist' mentioned in this thread).
Hope this saves you a journey down the M1.
Cheers,
Mark