Getting a Koetsu Onyx cartridge rebuilt - help

I have a vintage Koetsu Onyx that I'd like to have rebuilt. I don't want to use Van de Hul or Benz Micro because I don't want a hybrid back. Seem to recall reading somewhere that Koetsu has a service in London, or at least an arrangement with someone there who can do this type of work.

Any help would be greatly appreciated.

Doug