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 DiscLubrication
Lubrication is necessary after riding
through rain or on wet roads, or any
time that the chain appears dry.
Use a lubricant for sealed chains to
prevent deterioration of chain seals. If
the chain is especially dirty, clean it
using a cleaner for sealed chains following
the instructions suppli ...
Crankshaft Sensor Removal
Remove:
Fuel Tank (see Fuel Tank Removal in the Fuel System
(DFI) chapter)
Crankshaft Sensor Lead Connector [A]
Remove:
Right Lower Fairing (see Lower Fairing Removal in the
Frame chapter)
Bolts [A]
Crankshaft Sensor Cover [B] and Gasket
Oil Pressure Switch Terminal [C]
...
Exhaust Pipe Removal
Remove:
Radiator (see Radiator and Radiator Fan Removal in the
Cooling System chapter)
Exhaust Pipe Clamp Bolt [A] (Loosen)
Remove the exhaust pipe holder nuts [A], and pull out the
exhaust pipe [B] forward from the premuffler chamber.
...