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 DiscRear Shock Absorber Inspection
Press down on the seat several times
to inspect the stroke.
Visually inspect the rear shock absorber
for oil leaks.
If there is any doubt about the rear
shock absorber, it should be inspected
by an authorized Kawasaki
dealer.
A. Rear Shock Absorber
Spring Preload Adjustment
...
Key Registration
Case 1: When the ignition key has been lost or additional
spare ignition key is required.
Prepare a new spare ignition key.
Cut the key in accordance with the shape of the current
ignition key.
Remove the rear seat (see Rear Seat Removal in the
Frame chapter).
Remove the immobilizer/K ...
Camshaft, Camshaft Cap Wear Inspection
Remove the camshaft caps (see Camshaft Removal).
Cut the strips of plastigage (press gauge) to journal width.
Place a strip on each journal parallel to the camshaft installed
in the correct position.
Tighten the camshaft cap bolts and upper camshaft chain
guide bolts to the specified ...