If they appear damaged or deteriorated, replace them.

Balancer Adjustment
Torque LimiterWiring Diagram (Other than US, CA and CAL without KIBS Models)
ZX1000JC
ZX1000JD
...
Front Master Cylinder Removal
Remove the reservoir mounting bolt and nut [A].
Unscrew the banjo bolt [A] and disconnect the brake hose
from the master cylinder (see Brake Hose and Pipe Replacement
in the Periodic Maintenance chapter).
Unscrew the clamp bolts [B], and take off themaster cylinder
as an assembl ...
Valve Guide Installation
Apply engine oil to the valve guide outer surface before
installation.
Heat the area around the valve guide hole to about 120
150°C (248 302°F).
NOTICE
Do not heat the cylinder head with a torch. This will
warp the cylinder head. Soak the cylinder head and
heat the oil.
Usin ...