2005 Cadillac STS Owner's Manual - Page 336

Front Axle When to Check and Change Lubricant It is not necessary to regularly check the front 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 repaired. 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, located on the front axle, you may need to add some lubricant. What to Use Refer to the Maintenance Schedule to determine what kind of lubricant to use. See Recommended Fluids and Lubricants on page 6-12. How to Check Lubricant A. Drain Plug B. Filler Plug 5-46