[RodB]

Roy,

That slot on the back is a screw adjustment to put tension on the shaft of the rotor. The nut tightens to hold the screw in place. Adjustment of this is rarely needed. Mike suggested putting lubrication on the other side where the screw meets the rotor shaft. The front end of the shaft is likely where the bearings are. They probably have old dried up grease causing the stiffness. The rotor should move smoothly throughout it's rotation without much resistance yet not floppy and loose.