Hi Barry, I presume that the black plastic segment is still present and intact, which is in the top of the bore that the carriage slides along the bed on. Seen in the photo below with masking tape on.

There should also be one in the tailstock. However, as has been said, the adjustment is very finely balanced between being too tight or too loose. Otherwise you may have serious wear in one or the other or both.
Regards Nick.
Edited By Nicholas Farr on 29/04/2019 07:13:15