The rear axle pinion seal may leak causing fluid loss and possible internal rear end damage. Replacing the faulty seal will commonly correct this concern.
Car Problem Reports
Cadillac STS Rear Axle Pinion Seal May Leak
Cadillac STS Problem
Average Mileage: 41,440 mi (21,000 mi - 73,000 mi)
Visitor, 2009 Cadillac STS
just brought car , only put @ 100 miles on it and found little drop of oil on garage floor it came from rear axle its at dealership now didnt have chance to purchase extended warranty hopiing they will fix it
Visitor, 2005 Cadillac STS, 21,000 mi
Bought this car used with 18000 miles on it, and the rear pinion seal let go shortly after that. The selling dealer replaced it, and so far, at 27000 it is still OK. However, the rear end hums between 35 and 50 mph.