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 DiscShifting Gears
Close the throttle while pulling in the
clutch lever.
Shift into the next higher or lower
gear.
Open the throttle part way, while releasing
the clutch lever.
For smooth riding, each gear position
should cover the proper rate of speed
shown in the table.
WARNINGDownshifti ...
Front Fender Removal
Remove:
Bolts [A] with Washers (Both Sides)
Reflectors (Both Sides, US, CA, CAL and AU Models)
Front Fender [B]
Take the brake hose off the clamp [C] (both sides).
Front Fender Installation
Apply a non-permanent locking agent to the front fender
mounting bolts.
Tighten:
...
Front Master Cylinder Removal
Remove the reservoir mounting bolt and nut [A].
Unscrew the banjo bolt [A] and disconnect the brake hose
from the master cylinder (see Brake Hose and Pipe Replacement
in the Periodic Maintenance chapter).
Unscrew the clamp bolts [B], and take off themaster cylinder
as an assembl ...