At last, bike back from sgs with the gearbox in and working. I had her out all day yesterday and she is amazing.
Still unsure what was wrong but I know they've removed the outer washer from the selector drum as well as a problem with selectors.
I find it hard to believe that a precision piece of equipment can vary from bike to bike, some bikes have washers and some don't?
Anyway it's fixed so I'll just enjoy it while I can.
Can't thank Ian at sgs and Duncan for their help, knowledge and effort taken to get things back to me.