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 DiscWarning/Indicator Lights
: When the
transmission is in
neutral, the neutral indicator light goes
on.
: When the
headlight is on high
beam, the high beam indicator light
goes on.
: When the
turn signal switch is
pushed to the left or right, the turn signal
indicator light blinks. ...
Coolant Deterioration Inspection
Remove the right lower fairing (see Lower Fairing Removal
in the Frame chapter).
Visually inspect the coolant in the reserve tank [A].
If whitish cotton-like wafts are observed, aluminum parts
in the cooling system are corroded. If the coolant is
brown, iron or steel parts are rusting. I ...
Special Tools and Sealants
Outside Circlip Pliers:
57001-144
Piston Pin Puller Assembly:
57001-910
Piston Ring Compressor Grip:
57001-1095
Piston Ring Compressor Belt, 67
79:
57001-1097
Bearing Driver Set:
57001-1129
Liquid Gasket, TB1216B:
92104-1064
Liquid Gasket, TB1207B:
92104-2068
...