[Lynn Eades]

A modern brand name thrust bearing will normally last the life of the clutch plate and eliminates the possibility of over greasing, which can happen.
However the grease supply also lubes the bearing support, which otherwise can only be achieved on assembly. I think there are probably two bearing types. one is sealed and lubed for the life of the bearing. the second is open where it rides on the support, or has a hole in that position for the grease to get into the bearing.