Finally finished my wheels. I've discovered however, after looking closer at the parts diagram for the rear hub, there is supposed to be a fibre washer behind the rear sprocket before you bolt onto the wheel.
What is it's function? Stop grease getting into the brakes, or stop brake dust getting into bearings...? I seem to remember the bearing on this side already has a fibre washer fitted inside the little 'cup' which should stop significant grease transfer?
Ok, a felt washer I guess it had more or less the same job as a modern day oil seal. Keeping the grease in and / or the dirt out. I would fit one anyway.