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 DiscWater Temperature Sensor Output Voltage Inspection
NOTE
Be sure the battery is fully charged.
Turn the ignition switch to OFF.
Remove the throttle body assy (see Throttle Body Assy
Removal in the Fuel System (DFI) chapter).
Disconnect the water temperature sensor connector and
connect the measuring adapter [A] between these connectors
...
Intake Air Pressure Sensor #1 Input Voltage Inspection
NOTE
Be sure the battery is fully charged.
Turn the ignition switch to OFF.
Remove the air cleaner housing (see Air Cleaner Housing
Removal in the Fuel System (DFI) chapter).
Disconnect the intake air pressure sensor #1 connector
and connect the measuring adapter [A] between these
con ...
Oil Filter Replacement
Drain the engine oil (see Engine Oil Change).
Remove the left lower fairing (see Lower Fairing Removal
in the Frame chapter).
Remove the oil filter [A] with the oil filter wrench [B].
Special Tool - Oil Filter Wrench: 57001-1249
Replace the filter with a new one.
Apply grease t ...