Remove the impeller screw and flat washer.
Put red thread locking compound around the edge of the impeller shaft. 
Slide the impeller up and down on the shaft. Make sure that the locking compound is spread evenly on the shaft and the inside of the bore of the impeller.
Put red thread locking compound on the impeller screw .
Install the screw  and the flat washer .
Note: Turn the impeller screw counterclockwise to tighten it.
Align the marks on the cover and the pump body.
Install the impeller cover with the (3) screws and (3) lock washers.