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 DiscIgnition Switch Replacement
Remove:
Air Cleaner Housing (see Air Cleaner Housing Removal
in the Fuel System (DFI) chapter)
Disconnect the lead connectors [A].
Remove:
Steering Stem Head (see Stem, Stem Bearing Removal
in the Steering chapter)
Using a small chisel or punch [A], turn out the Torx bolts.
...
System Components
1. FI ECU
The FI ECU analyzes the motorcycle conditions based
on the signals from the front/rear wheel rotation sensors
and FI sensors (such as the crankshaft sensor and main
throttle sensor), and controls engine power by reducing the
number of ignition and retarding the ignition timing. The
m ...
Wheel Inspection
Raise the front/rear wheel off the ground.
Special Tools - Jack: 57001-1238
Jack Attachment: 57001-1608
Spin the wheel lightly, and check for roughness or binding.
If roughness or binding is found, replace the hub bearings
(see Hub Bearing Removal/Installation).
Inspect the wh ...