I had an S-Tec 30 in my last aircraft - it had been installed by Tatenhill, so I suppose that they must be able to service these?
Peter is right though for the older autopilots - my KFC 200 went back to a well known avionics supplier, who then mailed it on to a specialist in the USA for repair. I went down that route, rather than going direct, so that the repair came with the right paperwork...!
