It was Sunday, I drained the oil (Chevron ESI 80W-90) out of the diff of my 2005 Honda S2000 and replaced it with the same Chevron ESI 80W-90.
The car had only 15,000 miles when I got it last year ... but I was anxious to replace all the fluids ... including the diff and manual tranny. It was a good thing, too. The diff came out really nasty looking. Dark and thick with lots of wear particles and a real mess on the magnetic drain plug. I refilled with .9 of a quart of Chevron ESI 80W90 and vowed I would run it one year and drain again as a flush. 2nd drain last weekend looked better ... but still plenty grey.
I will now run the current fill for 10,000-15,000 miles and do a UOA to see how this oil holds up in this notoriously inhospitable torsen diff. This should take about 3 years.