If a master cylinder or piston shows any damage, replace them.

If a cup is worn, damaged softened (rotted), or swollen, the piston assembly should be replaced to renew the cups.
If fluid leakage is noted at the brake lever, the piston assembly should be replaced to renew the cups.
If they are damaged, replace them.
If the springs are damaged, replace them.
If the relief port becomes plugged, the brake pads will drag on the disc. Blow the ports clean with compressed air.
Front Master Cylinder [I] Rear Master Cylinder [J]

Rear Master Cylinder Installation
Brake DiscConnecting Rod Bend Inspection
Remove the connecting rod big end bearing inserts, and
reinstall the connecting rod big end cap.
Select an arbor [A] of the same diameter as the connecting
rod big end, and insert the arbor through the connecting
rod big end.
Select an arbor of the same diameter as the piston pin
and ...
What is a Limited Warranty?
The most important thing to know about your warranty is that it protects you
from manufacturing defects in material or workmanship during the warranty
period.
You can find the warranty period in the Kawasaki Limited Warranty Certificate
your Kawasaki dealer provided to you at the time of sale ...
Engine Sprocket Removal
Remove:
Engine Sprocket Cover Bolts [A]
Engine Sprocket Cover [B]
Flatten out the bended washer [A].
Remove the engine sprocket nut [B] and washer.
NOTE
When loosening the engine sprocket nut, hold the rear
brake on.
Raise the rear wheel off the ground with the stand. ...