An update, the Leica Forum very kindly recommended two repairers in Europe, van Manen Kamera Repair in the Netherlands and Paepke in Germany. The latter wanted to see the camera before quoting (which is understandable) but would charge €45 if I didn't proceed with a repair with them. Add in postage at each end and my enthusiasm for this route is limited.
Cathy Kuiper at van Manem thought it had not been serviced for some time, and said because of the mechanical complexity it would be €235 plus disbursements plus VAT, with a turnaround time of a month (usual caveats about unforeseen issues).
My experience with Newton Ellis would be they would do a super job, but Ian is snowed and my last lens (a dual range Summicron) took 9 months. I could well believe the same timetable might apply with this thing.
The US option lacks appeal as shipping is not cheap and I will be liable for import duty and VAT on the repairs, plus courier handling charges.
Cathy Kuiper has done work for Erik van Straten here and van Manen have an excellent reputation, so they will likely get the business when I get round to sending it over. I can't find a replacement at anything like this cost in the condition mine is in, and I think a service on this camera, which I love more than my non-existent children, would see me and it through for a long time.