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 DiscAir Intake Duct Disassembly
(Other than US, CA and CAL Models)
Remove:
Air Intake Duct (see Air Intake Duct Removal)
Seal [A] and Screen [B]
Turn the air intake valve actuator [C] counterclockwise
(90°).
Remove the shaft [A] of the air intake valve actuator.
Remove:
Pad [A]
Screws [B]
Air Intake Valve [C]
...
Balance Weight Installation
Check if the weight portion has any play on the blade [A]
and clip [B].
If it does, discard it.
WARNINGUnbalanced wheels can create an unsafe
riding
condition. If the balance weight has any play on
the rib of the rim, the blade and/or clip have been
stretched. Replace th ...
Stator Coil Installation
Apply a non-permanent locking agent to the threads of
the stator coil bolts and tighten them.
Torque - Stator Coil Bolts: 12 N·m (1.2 kgf·m, 106 in·lb)
Using a high flash-point solvent, clean off any oil or dirt
that may be on the silicone sealant coating area. Dry
them with a clea ...