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 DiscShift Pedal Installation
Install the rubber damper to the shift pedal.
Turn the chamfered side to inside.
Assemble:
Shift Lever [A] and Locknut [B] (Left-hand Thread)
Shift Pedal [C] and Locknut [D]
Tie-Rod [E]
Turn the grooved end [F] of the tie-rod to the shift lever.
Apply grease to the sliding ...
Brake Line Bleeding
The brake fluid has a very low compression coefficient so
that almost all the movement of the brake lever or pedal
is transmitted directly to the caliper for braking action. Air,
however, is easily compressed. When air enters the brake
lines, brake lever or pedal movement will be partially used
...
System Components
1. KIBS ECU
With input from the front and rear wheel sensors and front
caliper hydraulic pressure, the KIBS ECU analyzes various
conditions on the motorcycle, and with additional information
from the FI ECU (engine speed, throttle position, gear
position, and clutch actuation) precisely control ...