Paranoia perhaps, but I sensed that the rear end was starting to whine just a bit. So at 60K miles I settled on the Redline 75W85 differential oil. Getting oil into the differential is another matter. Followed the advice to make sure the fill plug was loose. (14mm male hex head socket). I drilled a hole in the cap of the Redline bottle to accept a 1/4 pipe nipple attached to a piece of clear tubing. I was able to shove the bottle up in the suspension and hold it there with a bungie cord while it drained into the rear end. Since the oil is rather viscous, I punched a small hole in the bottle at its highest point allowing it to flow better. It would have been a lot handier to have some sort of pump or squeeze bottle. I will re-check the level next time the car is up in the air. Can't road test right now because of the road salt this time of year in my area.