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 DiscWiring Diagram (US, CA and CAL with KIBS Models)
ZX1000KC
ZX1000KD
...
City Light (LED) Removal/Installation
Remove:
Upper Fairing Assembly (see Upper Faring Assembly
Removal in the Frame chapter)
Headlight (see Headlight Removal)
Remove the screws [A], and take the city light [B] off the
upper fairing assembly.
Installation is the reverse of removal. Note the following.
When inst ...
Check 2-3: Intake Air Temperature Inspection
Disconnect the intake air temperature sensor connector
[A] (see Intake Air Temperature Sensor Removal in the
Self-Diagnosis System chapter).
Connect the variable rheostat [B] to the R/BK lead [C] and
BR/BK lead [D] terminals.
Turn the ignition switch to ON.
Read the temperatur ...