Agreed, the fluid in my differential was some kind of horrible, nasty jet black after only 12k miles and I dont track my car or do burnouts.
Bought two quarts of Redline 75W-90 (not MT-90) and two new differential bolt washers to be safe. Had no trouble draining the crud out and filling her up with good fluid.
DIY is here:
DIY: Rear Differential Oil Change
Fluid options are here:
Fluid Swap Discussions
Also, its worth noting that while the 2009 Owners manual asks for Super Hypoid 80W-90 Gear oil (GL-5), the 2010 manual says to use synthetic 75W-90 GL-5 gear oil. Logic says there is a reason it was changed so I would go with a nice synthetic 75W-90 GL-5 gear oil like Redline, Motul Gear 300, etc.