Well Patrick, as it turned out, I phoned the first company which was suggested on my flickr page, and to be honest, they werent all that enthusiastic about repairing it. Nightmare camera was mentioned. They told me to buy a Bronica EC instead.
However, the guy on the phone went and got a colleague, this chap then described what he would do first if I took it to them. They had an old Bronica of similar vintage on the shelf; he then talked me through the following process.
Take the lens off and remove the focusing helicoid, which was extremely stiff. Now remove the black base plate by removing two extremely small screws, these really needed an offset screw driver, and as such, was an absolute swine using my watchmakers drivers, once this plate was off, it revealed some rollers and black cloth.
Still following instructions, I placed the camera lens opening down on a soft towel, and using the heel of my hand, gave the camera a wallop on its tripod socket, followed by a vigorous shake, and voila one little screw fell out!
The screw is from a metal shim to do with the focusing screen, and is now in a plastic bag. As for the vignette, he thinks this was a just a glitch possibly due to the extreme cold and design of this camera.
20 minutes later Im that happy, Im on the phone thanking him.