Thanks all,
Jock is correct. That is the washer. The inner diameter seems a bit large to fit in that location, but I believe you. It also matches Phil's photo.
Looking at Phil's photo, it would also seem that I am missing the inner washer . It might be a grease seal which is listed in the parts manual. I have only 1, so if anyone has a spare one , I would be grateful. Otherwise , I could probably make up a flat washer to suit. The inner one is quite thin.
It now means that I have to disassemble the hub to fit the inner washer.
