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 DiscDaily Checks
Check the following items each day before you ride. The time required is
minimal,
and habitual performance of these checks will help ensure you a safe, reliable
ride.
If any irregularities are found during these checks, refer to the Maintenance
and
Adjustment chapter or see your dealer fo ...
Valve Clearance
Valve and valve seat wear decreases
valve clearance, upsetting valve timing.
NOTICE
If valve clearance is left unadjusted,
wear will eventually
cause the valves to remain
partly open; which lowers performance,
burns the valves and
valve seats, and may cause serious
engine damage.
Valve cle ...
DFI System Wiring Diagram (KIBS Equipped Models)
1. Air Intake Solenoid Valve (Other than US, CA and CAL Models)
2. Engine Stop Switch
3. Starter Button
4. Air Switching Valve
5. Stick Coil #1, #2, #3, #4
6. Spark Plugs
7. Intake Air Temperature Sensor
8. Crankshaft Sensor
9. Secondary Fuel Injector #1
10. Secondary Fuel Injector #2
...