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 DiscCAN Communication (Transmission)/CAN Bus OFF Monitor Inspection (Service Code
b 57) CAN Communication (Reception) Monitor Inspection (Service Code b 58)
Remove:
Seat (see Seat Removal in the Frame chapter)
Immobilizer (Equipped Models)/Kawasaki Diagnostic
System Connector Cap [A]
Measure the CAN communication line resistance.
Immobilizer (Equipped Models)/Kawasaki Diagnostic
System Connector [A]
GY/BL Terminal [B]
LB Ter ...
Nozzle Assy Assembly
Before assembling, blow away dirt or dust from the delivery
pipes [A] by applying compressed air [B].
Replace the O-rings [A] of the joint pipe [B] with new ones.
Apply engine oil to the new O-rings, and insert it to the
delivery pipes [C]
Insert the joint pipe so that the step ...
Front Seat Installation
Installation is the reverse of removal. Note the following.
Check that the dampers [A] are in place on the front seat.
Install the collars [B] as shown in the figure.
Place the seat hooks [A] under the fuel tank bracket [B].
...