Thanks guys,

Mike, the brakes are also leaking, presumably from the o ring/bellows. If I needed to change or check the bellows I can't see any way of removing them because that outer disc is fixed solid.
I see what you mean about the rubber bellows expanding into the wheel though. I would expect the rubber to wear out fast!
Do you mean use silicon on the wheels instead of an o ring?

Joe, thanks for links etc.

Regards to you both,
Gary.