Cadillac 2004 XLR - Manual (Page 269)

Rear Axle
When to Check Lubricant
It is not necessary to regularly check rear axle fluid
unless you suspect there is a leak or you hear an
unusual noise. A fluid loss could indicate a problem.
Have it inspected and repair.
How to Check Lubricant
To get an accurate reading, the vehicle should be on a
level surface.
If the level is below the bottom of the filler plug hole,
you will need to add some lubricant. Add enough
lubricant to raise the level to the bottom of the filler
plug hole.
What to Use
To add lubricant when the level is low, use
SAE 75W–90 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.
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