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 DiscInterlock Operation Inspection
Raise the rear wheel off the ground with the stand [A].
1st Check
Start the engine to the following conditions
Condition:
Transmission Gear → 1st Position
Clutch Lever → Release
Sidestand → Down or Up
Turn the ignition switch to ON and push the starter butto ...
Master Cylinder Rubber Parts Replacement
Front Master Cylinder Disassembly
Remove the front master cylinder (see Front Master Cylinder
Removal in the Brakes chapter).
Remove the seal cover [A], circlip [B], connector [C] and
O-ring [D].
Special Tool - Inside Circlip Pliers: 57001-143
Unscrew the locknut [E] and pivot bolt ...
Radiator and Radiator Fan Removal
Remove:
Upper Fairing Assembly (see Upper Fairing Assembly
Removal in the Frame chapter)
Coolant (Drain, see Coolant Change in the Periodic
Maintenance chapter)
Air Cleaner Housing (see Air Cleaner Housing Removal
in the Fuel System (DFI) chapter)
Coolant Reserve Tank (see Coolant R ...