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 DiscSpecial Tools and Sealant
Oil Pressure Gauge, 10 kgf/cm²:
57001-164
Oil Pressure Gauge Adapter, PT3/8:
57001-1233
Outside Circlip Pliers:
57001-144
Liquid Gasket, TB1211:
56019-120
...
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 ...
Rear Fender Front Installation
Installation is the reverse of removal. Note the following.
Run the harness, cables and leads correctly (see Cable,
Wire, and Hose Routing section in the Appendix chapter).
When installing the clamp [A] on the rear fender front [B],
install it so that the clamp positions at near the ...