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 DiscThermostat Inspection
Remove the thermostat (see Thermostat Removal).
Inspect the thermostat valve [A] at room temperature.
If the valve is open, replace the thermostat with a new
one.
To check valve opening temperature, suspend the thermostat
[A] in a container of water and raise the temperature
of ...
Coupling Bearing Installation
Replace the bearing with a new one.
Press in the bearing [A] until it is bottomed.
Special Tool - Bearing Driver Set [B]: 57001-1129
Pack the bearing with high-temperature grease.
Replace the circlip with a new one.
Special Tool - Inside Circlip Pliers: 57001-143
Replace the grease se ...
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 ...