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 DiscPrecautions
There are a number of important precautions that are
musts when servicing electrical systems. Learn and observe
all the rules below.
Do not reverse the battery cable connections. This will
burn out the diodes on the electrical parts.
Always check battery condition before condemning other
...
Rear Shock Absorber Removal
Remove:
Lower Fairings (see Lower Fairing Removal in the Frame
chapter)
Fuel Tank (see Fuel Tank Removal in the Fuel System
chapter)
Bolts [A] (Both Sides)
Foot Guard [B] (Both Sides)
Squeeze the brake lever slowly and hold it with a band
[A].
WARNINGBe sure to h ...
Specifications
Whenever you see the symbols
shown below, heed their instructions!
Always follow safe operating and maintenance
practices.
DANGER
DANGER indicates a hazardous
situation which, if not avoided,
will result in death or serious injury.
WARNINGWARNING indicates a hazardous
situation whi ...