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 DiscSubthrottle Valve Actuator Inspection
NOTE
Be sure the battery is fully charged.
Remove the air cleaner housing (see Air Cleaner Housing
Removal in the Fuel System (DFI) chapter).
Turn the ignition switch to ON.
Check to see that all the subthrottle valves [A] open and
close smoothly.
Turn the ignition switch to OFF.
I ...
Oil Pressure Relief Valve Inspection
Remove the oil pressure relief valve (see Oil Pressure
Relief Valve Removal).
Check to see if the valve [A] slides smoothly when pushing
it in with a wooden or other soft rod, and see if it comes
back to its seat by spring [B] pressure.
NOTE
Inspect the valve in its assembled stat ...
Upper Fairing Assembly Removal
Remove:
Lower Fairings (see Lower Fairing Removal)
Center Inner Fairing (see Center Inner Fairing Removal)
Upper Inner Fairings (see Upper Inner Fairing Removal)
Windshield (see Windshield Removal)
Disconnect the front turn signal light lead connector [A]
(both sides).
Remove the bo ...