If the surface is corroded or if the blades are damaged, replace the impeller

Water Pump Impeller Disassembly/Assembly
Water Pump Housing DisassemblyLights and Switches Operation Inspection
First Step
Set the gear position in the neutral position.
Turn the ignition switch to ON.
The following lights should go on according to below table.
If the following light does not go on, inspect the meter
unit (see Meter Unit Inspection in the Electrical System
chapter).
...
Swingarm Removal
Remove:
Rear Wheel (see Rear Wheel Removal in the
Wheels/Tires chapter)
Mud Guard with Rear Brake Hose (see Mud Guard Removal
in the Frame chapter)
Rocker Arm (see Rocker Arm Removal)
Remove:
Brake Hose Clamp Bolt [A]
Unscrew the swingarm pivot shaft nut [A].
Usi ...
Transmission Shaft Assembly
Apply molybdenum disulfide oil solution to the sliding surfaces
of the gears and shafts.
Install the gears and the gear bushings [A] with their holes
[B] aligned.
Replace any circlips removed with new ones.
Install the circlips [A] so that the opening [B] of it is aligned
with ...