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 DiscTurn 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 ...
Piston Ring Groove Width Inspection
Measure the piston ring groove width.
Use a vernier caliper at several points around the piston.
Piston Ring Groove Width
Standard:
Top [A] 0.82 0.84 mm (0.0323
0.0331 in.)
Second [B] 0.82 0.84 mm
(0.0323 0.0331 in.)
Service Limit:
0.92 mm (0.036 in.)
Second 0.92 mm (0.036 in.)
...
Water Pump Inspection
Remove the left lower fairing (see Lower Fairing Removal
in the Frame chapter).
Check the drainage outlet passage [A] at the bottom of
the water pump body for coolant leaks.
If the mechanical seal is damaged, the coolant leaks
through the seal and drains through the passage. Replace
th ...