differential stain

[delinquent543]

I have a 2000 Trans am a4 with a little under 60,000 miles on it. I just got 2 new back tires put on and while it was on the lift, i noticed a stain on the rear differential (not a leak). There are no spots on my driveway from a leak, and it doesnt feel as if there are any problems when i drive it. I generally drive aggressive, but not all of the time. I got the car about 2 months ago, and when it was on the lift at the dealer, there was nothing there, but i am hearing all these 10-bolt horror stories, i really dont want to blow my differential any time soon. The car is mainly stock, except for an exhaust system. Ultimately i am asking if i should be worried at all. Also, there is a distinct whine coming from the engine when i accelerate, but all my mechanic said was to take it back if it gets any worse (which it hasnt), is that anything to worry about?

[dmnall]

It could be the pinion seal starting to leak. You can tell by looking behind the pinion (where the driveshaft bolts to the rear end) and see if the stain is there. The pinion seal is common, I had the one on my 02 Z28 replace 2x in the time I had my car.

Charlie