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 DiscSafe riding technique
The points given below are applicable for everyday motorcycle use and
should
be carefully observed for safe and effective vehicle operation.
For safety, eye protection and a
helmet are strongly recommended.
You should be aware of and verify
the applicable safety regulations in
force prior ...
Wiring Diagram (Other than US, CA and CAL without KIBS Models)
ZX1000JC
ZX1000JD
...
Special Tools
Inside Circlip Pliers:
57001-143
Oil Seal & Bearing Remover:
57001-1058
Bearing Driver Set:
57001-1129
Jack:
57001-1238
Bearing Remover Head, 15 ×
17:
57001-1267
Fork Oil Level Gauge:
57001-1290
Bearing Remover Shaft, 13:
57001-1377
Fork Oil Seal Driver, 43:
57001-15 ...