The stainless rotor shaft for the Rena Filstar XP filters rarely needs replacing. The shaft centers the rotor/impeller in the filter motor to achieve an efficient and smooth running system. The shaft terminates in the rotor-well bearing (black rubber bearing/bushing) at one end and the impeller cover at the other end. The impeller cover also has a bearing in the center to hold the shaft. The rubber bearings also absorb vibration for quieter operation. Older versions of the Rena Filstar XP Filter do not have the bearing in the impeller cover.