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 DiscFlap and Rear Fender Rear Removal
Remove:
Front and Rear Seat (see Front/Rear Seat Removal)
Seat Covers (see Seat Cover Removal)
Vehicle-down Sensor Connector [A]
Screws [B]
Clear the seat lock cable [C] from the seat lock unit [D].
Take off the seat lock unit and the bracket.
Remove:
Bolts [A] (Both Sides ...
Intake Air Pressure Sensor #1 Installation
NOTE
The intake air pressure sensor #1 is the same part as
the intake air pressure sensor #2.
Installation is basically the reverse of removal.
Position the intake air pressure sensor #1 [A] between the
projections [B] on the rubber damper.
Install the rubber damper [A] on the bracket ...
Crankcase Splitting
Remove the engine (see Engine Removal in the Engine
Removal/Installation chapter).
Set the engine on a clean surface and hold the engine
steady while parts are being removed.
Remove:
Cylinder Head (see Cylinder Head Removal in the Engine
Top End chapter)
Starter Motor (see Starter M ...