If any is worn down to the service limit, replace the brush assy.
Starter Motor Brush Length [B] Standard: 12.05 mm (0.4744 in.) Service Limit: 6.55 mm (0.258 in.)

Starter Motor Assembly
Commutator Cleaning and InspectionClutch Cover Installation
Using a cleaning fluid, clean off any oil or dirt that may
be on the silicone sealant coating area. Dry them with a
clean cloth.
Apply silicone sealant to the area [A] where the mating
surface of the crankcase touches the clutch cover gasket.
Sealant - Liquid Gasket, TB1211F: 92104-000 ...
Throttle Grip and Cables
Free Play Inspection
Refer to the Throttle Control System Inspection in the Periodic
Maintenance chapter.
Free Play Adjustment
Refer to the Throttle Control System Inspection in the Periodic
Maintenance chapter.
Cable Installation
Install the throttle cables in accordance with the Cable,
...
KIBS Hydraulic Unit Inspection
Remove the KIBS hydraulic unit (see KIBS Hydraulic Unit
Removal).
Visually inspect the connector terminals [A].
Replace the KIBS hydraulic unit or main harness if either
of the terminals are cracked, bent, or otherwise damaged.
If the KIBS hydraulic unit connector is clogged with mud
or ...