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 DiscFuel Injector Output Voltage Inspection
NOTE
Be sure the battery is fully charged.
Turn the ignition switch to OFF.
Remove the ECU (see ECU Removal).
Do not disconnect the ECU connector
Connect a digital meter [A] to the connector (gray) [B] with
the needle adapter set.
Special Tool - Needle Adapter Set: 57001-1457
...
Idle Speed Control Valve Actuator Removal
NOTICE
Never drop the idle speed control valve actuator especially
on a hard surface. Such a shock to the actuator
can damage it.
Remove:
Throttle Body Assy (see Throttle Body Assy Removal in
the Fuel System (DFI) chapter)
Idle Speed Control Valve Actuator Retainer Screws [A]
Idle Spe ...
Rear Fender Front Removal
Remove:
Flap and Rear Fender Rear (see Flap and Rear Fender
Rear Removal)
Fuel Tank (see Fuel Tank Removal in the Fuel System
(DFI) chapter)
Battery (see Battery Removal in the Electrical System
chapter)
Exhaust Butterfly Valve Actuator (see Exhaust Butterfly
Valve Actuator Remova ...