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 DiscTie-Rod Removal
Squeeze the brake lever slowly and hold it with a band
[A].
Remove the front footpeg bracket bolts [A].
Raise the rear wheel off the ground with the jack (see
Rear Shock Absorber Removal).
Special Tools - Jack: 57001-1238
Jack Attachment: 57001-1608
Remove:
Upper ...
Camshaft, Camshaft Cap Wear Inspection
Remove the camshaft caps (see Camshaft Removal).
Cut the strips of plastigage (press gauge) to journal width.
Place a strip on each journal parallel to the camshaft installed
in the correct position.
Tighten the camshaft cap bolts and upper camshaft chain
guide bolts to the specified ...
Gear Position Switch Installation
Securely place the springs [A] and pins [B] into the holes
[C] of the shift drum.
Apply grease to the new O-ring [D].
Install the gear position switch [E].
Apply a non-permanent locking agent to the threads of
the gear position switch screws [F].
Tighten:
Torque - Gear Position Swit ...