Yep, he is a good bloke.
Seeing you have had this issue from when you got the bike, the parts John points out need to be checked.
I have 2 parts lists for the 1100 (and early version and later with revised parts as well) which show the clutch differently depending on the engine number:
This is the earlier parts list with only upto engine number 158879 parts shown and this is the later parts list that shows both options - up to engine number 158879 and after. In the second you can see part 3 varies depending on which engine you have and that was John's issue - he had the wrong one in for his engine number. You can also see that the later engine number needs shims (item 4) that need to be calculated as well.
Reading your initial post it is possible in a rebuild someone has mixed and matched the clutch parts and hence why you have this issue. I hope so as then you are on the road to having it fixed.
The test (I think) for if it is that, is take out the fibre and steel clutch plates and can you turn the crank and basket without centre turning? If not it must be those parts. If you can, well check them anyway!
Thanks
UB