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 DiscFront, Rear Wheel Rotation Difference Abnormal Inspection (Service Code b
25)
Check the following and correct the faulty part.
Incorrect Tire Pressure
Tires not recommended for the motorcycle were installed
(incorrect tire size).
Deformation of Wheel or Tire
Missing Teeth or Clogging with Foreign Matter of Sensor
Rotor (see Wheel Rotation Sensor Rotor Inspe ...
Fuel Pump Operating Voltage Inspection
NOTE
Be sure the battery is fully charged.
Turn the ignition switch to OFF.
Remove:
Fuel Tank Bolts (see Fuel Tank Removal)
Fuel Tank Bracket Bolts (see Fuel Tank Removal)
Disconnect the fuel pump lead connector and connect the
harness adapter [A] between these connectors as shown
i ...
Front Caliper Removal
Remove:
Bolt [A]
Front Wheel Rotation Sensor [B]
Loosen the banjo bolt [C] at the brake hose lower end,
and tighten it loosely.
Unscrew the caliper mounting bolts [D], and detach the
caliper [E] from the disc.
NOTICE
Do not loosen the caliper assembly bolts [F]. Take
out only ...