Check if there is any wet spot at the seals before you change the fluid.
Mine developed a wet spot around a seal. Replaced it at dealer under powertrain warranty.
Just changed mine yesterday. It is not difficult, however, there is not much room to tip up the bottle so you can get the new fluid in. I bought one of the screw on tops with the tube connected to it so I could squeeze the bottle and get the fluid in. I used a fully synthetic fluid that was a little more expensive but I figured I would go with the best I could get since I was only changing it every 60K miles.
Are yoiu guys talking about an all wheel drive system? OR are you meaning the transmission oil? The front wheel drive X9 doesn't have a "rear end" otherwise.
or use Motul Gearbox 80W-90 (mineral)
The molybdenum bisulphide is a solid additive which gives very high
resistance under heavy working conditions of use.
Extreme pressure, anti-wear, anti-corrosion and anti-foam.
For all gearboxes and hypoid rear axles without limited slip systems.
Performance Standards: API GL4 and GL5 / MIL-L-2105D
Very high lubricating power which decreases friction and wear.
Thermal stability under high temperature.