After about 2 years after the rear differential pinion seal went and leaked out all of it’s fluid, I finally bit the bullet and had the whole thing replaced. After the seal went, I had the seal replaced and new fluid added. The differential then had a slight grating sound which was tolerable. In the past couple months, that turned into a turbine sounding whine that completely intolerable. That was pretty much the death knell for the rear differential. I was afraid it would lock up while driving with disastrous results or that it would end up stuck in the garage with locked wheels. A rebuilt differential was ordered and installed. The rebuilt unit was about $1175 with a couple hundred added for shipping. 13 hours labor resulted in everything back to normal. The rear is now dead quiet and the car drives like a dream.