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 DiscCable Removal
Remove:
Air Cleaner Housing (see Air Cleaner Housing Removal
in the Fuel System (DFI) chapter)
Right Lower Fairing (see Lower Fairing Removal in the
Frame chapter)
Loosen the nuts [A], and slide the lower end of the clutch
cable to give the cable plenty of play.
Screw in the ...
Passenger’s Seat Removal
Remove the passenger’s seat by inserting
the ignition key into the seat
lock, and turning it clockwise.
A. Seat Lock
B. Ignition Key
C. Passenger’s seat
D. Pull up
NOTE
When removing the passenger’s
seat, pull it up while turning the key. ...
Wheel/Tire Damage Inspection
Remove any imbedded stones [A] or other foreign particles
[B] from tread.
Visually inspect the tire for cracks and cuts, and replace
the tire if necessary. Swelling or high spots indicate internal
damage, requiring tire replacement.
Visually inspect the wheel for cracks, cuts and dents ...