My vote goes to Newton Ellis - they have worked their way through numerous Leicas, Nikon F3s and view camera shutters for me, good job every time, and do not shrink from "difficult" cameras like Kodak Retina Reflexes which other repairmen will not touch (the NE guys are enthusiastic users of old cameras).

They did a Day studio shutter for me, too, which is quite an obscure item. Their self-imposed standards are very high - once an extractor tool broke while they were trying to unscrew an optical group from a view camera lens, resulting in a very small scratch to an internal glass surface which I couldn't even see - nonetheless, they apologised and refused payment for this job.