Repairing Tilt Swivel  

I own a Mr Plycraft chair by George Mulhauser. The swivel is so stiff that it needs repairing or replacement of the whole assembly. I would like to take it apart and clean the shaft, but find it nearly impossible to remove from the base. I need to remove it in order to replace a teflon ring at the top that acts to lubricate the contact with the hardware.
Can the shaft be removed? If I decide to repace the hardware, is it available and can it be replaced without purchasing the base as well?