Chevrolet 1999 Corvette Owner's Manual page 272

How to Check Lubricant
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.
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What to Use
To add lubricant when the level is low, use SAE 75W
Synthetic Gear Lubricant (GM Part No. 12378261) or
equivalent meeting GM Specification 9986115. To
completely refill after draining, add 4 ounces (118 ml)
-
of Limited Slip Differential Lubricant Additive
(GM Part No. 1052358) or equivalent. Then fill to
the bottom of the filler plug hole with the Synthetic
Gear Lubricant.
Surge Tank Pressure Cap
NOTICE:
The surge tank pressure cap is a 15 psi (105 kPa)
-
pressure type cap and must be tightly installed to
prevent coolant loss and possible engine damage
from overheating.
When you replace the surge tank pressure cap, a GM cap
is recommended.
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