Replace it if necessary.

Inner Tube Inspection
Spring Tension InspectionCylinder Head Cover Installation
Replace the cylinder head cover gasket [A] with a new
one
Using a high flash-point solvent, clean off any oil or dirt
that may be on the silicone sealant coating area. Dry
them with a clean cloth.
Apply silicone sealant [B] to the cylinder head as shown
in the figure.
Sealant - Li ...
Rear Wheel Removal
Raise the rear wheel off the ground with the stand [A].
Remove:
Cotter Pin [A]
Rear Axle Nut [B]
Washer [C]
Rear Axle [D] (from Right Side)
Remove the rear wheel rotation sensor from the caliper
bracket (see Rear Wheel Rotation Sensor Removal in the
Brakes chapter).
...
Rear Sprocket Warp Inspection
Raise the rear wheel off the ground with the stand so that
it will turn freely.
Set a dial gauge [A] against the rear sprocket [B] near the
teeth as shown in the figure, and rotate [C] the rear wheel
to measure the sprocket runout (warp). The difference
between the highest and lowest di ...