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 DiscCrankshaft Sensor Installation
Apply a non-permanent locking agent to the crankshaft
sensor bolts [A].
Tighten:
Torque - Crankshaft Sensor Bolts: 5.9 N·m (0.60 kgf·m, 52
in·lb)
Using a high flash-point solvent, clean off any oil or dirt
that may be on the silicone sealant coating area. Dry
them with a clean cl ...
Front Seat Installation
Installation is the reverse of removal. Note the following.
Check that the dampers [A] are in place on the front seat.
Install the collars [B] as shown in the figure.
Place the seat hooks [A] under the fuel tank bracket [B].
...
Steering Damper Installation
Install the following parts as shown in the figure.
Collar [A]
Washer (t = 3.5 mm, 0.14 in.) [B]
Steering Damper [C] (
ZX1000JC/KC)
Electronic Steering Damper [D] (ZX1000JD/KD)
Washer (t = 1.2 mm, 0.05 in.) [E]
Apply a non-permanent locking agent to the threads of
the steering ...