I have a Hall 9619ST swivel-tilt chair that is 12 years old (Aug 2005). It has a screw-jack type height adjust. There is the mechanism that tilts which is attached to the chair seat. This mechanism has a threaded rod that extends into the base with casters. There is a plastic liner insert in this base that makes contact with the threaded rod. I think this is the part that is worn out that I would like to replace. Anyone ever had this problem before?