I can't answer your question but I would suggest rather than trying to repair a 43 year old piece of electronics which is based on 50 year old technology, you seriously consider upgrading to a modern autopilot. A fellow I know spent over $ 10,000 over 2 years trying to get his 400A Autopilot to work reliably and finally gave up and installed a STEC 60-2 which has worked perfectly since day 1. Fixing autopilots is not like fixing a com radio where you give the box to a tech and he fixes it. Autopilot repairs have to be approached as a whole of aircraft troubleshooting exercise. For example another friend with a King FFC 200 went through 3 shops trying to fix a pitch anomaly. Eventually the 3 rd shop found that there was nothing wrong with the autopilot, the problem was a severe under tension on the elevator control cables. When all of the control cable tensions were set up properly the autopilot worked fine.
Even if you get it working again a Navomatic 400 is still a Shyte autopilot with wobbly control and limited functionality.
If you still want to find an EU repair shop I suggest you repost this in the Private Flying forum.