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 DiscOil Level Inspection
Check that the engine oil level is between the upper [A]
and lower [B] levels in the gauge.
NOTE
Situate the motorcycle so that it is perpendicular to the
ground.
If the motorcycle has just been used, wait several minutes
for all the oil to drain down.
If the oil has just been changed, ...
Warning Indicator Light (LED)
Light (LED) Inspection
The warning indicator light (LED) [A] is used for the FI indicator,
immobilizer indicator (immobilizer equipped models),
water temperature warning indicator and oil pressure
warning indicator.
In this model, the warning indicator light (LED) (FI/immobilizer)
goes ...
Connecting Rod Big End Side Clearance Inspection
Measure connecting rod big end side clearance.
Insert a thickness gauge [A] between the big end and either
crank web to determine clearance.
Connecting Rod Big End Side Clearance
Standard: 0.13 0.38 mm
(0.0051 0.0150 in.)
Service Limit: 0.58 mm (0.023 in.)
If the clearance exceeds ...