GMC 1996 Sierra Owner's Manual page 275

Four-wheel Drive
Most lubricant checks in this section also apply to
four-wheel-drive vehicles. However, they have two
additional systems that need lubrication.
Transfer Case
M7hen to Check Lubricant
How to Check Lubricant
Refer to the Maintenance Schedule to determine how
often to check the lubricant. See "Periodic Maintenance
Inspections'' in the Index.
If the level is below the bottom of the filler plug hole,
you'll need to add some lubricant. Add enough lubricant
to raise the level to the bottom of the filler plug hole.
What to Use
Refer
to
the Maintenance Schedule to determine what
kind
of
lubricant to use. See "Recommended Fluids and
Lubricants" in the Index.
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