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 DiscMaster Cylinder Rubber Parts Replacement
Front Master Cylinder Disassembly
Remove the front master cylinder (see Front Master Cylinder
Removal in the Brakes chapter).
Remove the seal cover [A], circlip [B], connector [C] and
O-ring [D].
Special Tool - Inside Circlip Pliers: 57001-143
Unscrew the locknut [E] and pivot bolt ...
Turn Signal Relay Inspection
Remove the battery (see Battery Removal).
Take the turn signal relay [A] off the rear fender.
Disconnect the connector [B].
Connect one 12 V battery and turn signal lights as indicated
in the figure, and count how many times the lights
blink for one minute.
Turn Signal Relay ...
KIBS Servicing Precautions
There are a number of important precautions that should
be followed servicing the KIBS.
This KIBS is designed to be used with a 12 V sealed battery
as its power source. Do not use any other battery
except for a 12 V sealed battery as a power source.
Do not reverse the battery cable connec ...