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 DiscBrake Hose and Pipe Replacement
NOTICE
Brake fluid quickly ruins painted plastic surfaces;
any spilled fluid should be completely washed away
immediately.
Remove:
Upper Fairing Assembly (see Upper Fairing Assembly
Removal in the Frame chapter)
Brake Hose Fitting Bolt [A]
Brake Hose Banjo Bolts [B]
Bolt [C]
Clamp ...
Mode-switching
Depress the S-KTRC button on the left handlebar switch
to change the mode. The mode can be changed only when
the throttle grip is closed completely.
The S-KTRC OFF can be selected only when the motorcycle
is at a stop. Changing to mode 1 from S-KTRC OFF
is possible while riding.
NOTE
...
Oxygen Sensor Removal (Equipped Models)
Remove:
Fuel Tank (see Fuel Tank Removal in the Fuel System
(DFI) chapter)
Right Lower Fairing (see Lower Fairing Removal in the
Frame chapter)
Disconnect the oxygen sensor lead connector [A].
NOTICE
Do not pull strongly, twist, or bend the oxygen sensor
lead. This may cause the wi ...