Replace it if necessary.

Inner Tube Inspection
Spring Tension InspectionOil Level Inspection
Check that the engine oil level is between the upper [A]
and lower [B] levels in the gauge.
NOTE
Situate the motorcycle so that it is perpendicular to the
ground.
If the motorcycle has just been used, wait several minutes
for all the oil to drain down.
If the oil has just been changed, ...
Valve Removal
Remove the cylinder head (see Cylinder Head Removal).
Remove the valve lifter and shim.
Mark and record the valve lifter and shim locations so they
can be installed in their original positions.
Using the valve spring compressor assembly, remove the
valve.
Special Tools - Valve ...
Water Pump Housing Disassembly
NOTICE
Do not damage the hole wall of the water pump
housing.
Insert a bar [A] into the pump housing [B], and hammer
evenly around the circumference of the mechanical seal
bottom [C].
Take the oil seal [A] out of the housing [B] with a hook [C].
...