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 DiscOil Filter Replacement
Drain the engine oil (see Engine Oil Change).
Remove the left lower fairing (see Lower Fairing Removal
in the Frame chapter).
Remove the oil filter [A] with the oil filter wrench [B].
Special Tool - Oil Filter Wrench: 57001-1249
Replace the filter with a new one.
Apply grease t ...
Cylinder Head Installation
NOTE
The camshaft cap is machined with the cylinder head,
so if a new cylinder head is installed, use the cap that
is supplied with the new head.
Install the dowel pins.
Replace the cylinder head gasket with a new one.
Replace the cylinder head bolt washers with new ones.
Apply molybden ...
Air Intake Solenoid Valve Unit Test
Remove the air intake solenoid valve (see Air Intake Solenoid
Valve Removal in the Fuel System (DFI) chapter).
Set the hand tester [A] to the × 1 Ω range and connect it
to the air intake solenoid valve terminals as shown in the
figure.
Special Tool - Hand Tester: 57001-1394
...