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 InspectionDFI System Troubleshooting Guide
NOTE
This is not an exhaustive list, giving every possible cause for each
problem listed. It is meant
simply as a rough guide to assist the troubleshooting for some of the more
common difficulties in
DFI system.
The ECU may be involved in the DFI electrical and ignition system
tro ...
Special Tools and Sealant
Oil Pressure Gauge, 10 kgf/cm²:
57001-164
Oil Pressure Gauge Adapter, PT3/8:
57001-1233
Outside Circlip Pliers:
57001-144
Liquid Gasket, TB1211:
56019-120
...
Fuses
Fuses are arranged in the fuse boxes
located under the passenger’s seat and
in the left fairing. The main fuse is
located under the passenger’s seat.
If a fuse fails during operation, inspect
the electrical system to determine
the cause, and then replace it with
a new fuse of proper amp ...