I don't know of any places in Europe for LF shutter cleaning and adjusting. We have a wonderful place here, called Flutot Camera Repair (in California, US) and they are great. They fixed my Supermatic and made it like new.
If you really want to do it yourself though, I would suggest taking the lens cells off first. Then find some Naphta or Ronsonol (lighter fluid for the old style lighters) and spray some inside the shutter, followed by some compressed air. I tried, successfully, with another type of shutter (simpler) to submerge the entire shutter in a bath of Naphta. However, Supermatics are known to be sensitive. My recommendation would be doing it professionally.