I changed the front and rear differentials AWD (6,500 miles)
The rear differential was tightened by some gorilla because it was tough to break the plugs. Finally did it and drained it. There was about 1/4 inch of metal shavings on the magnet and the fluid was nasty. When clutch plates break-in, they release tons of debris before they get their mating and wear in pattern. I'm glad I changed the fluid.
The front differential was a lot easier to remove the plugs BUT the drain plug didn't tighten down with the torque wrench properly and left me uneasy. I think they over tightened it at the factory or the threads were not properly cut at the factory. So I put down about 2 wraps of TEFLON TAPE on the bottom drain plug. I hand tightened it with a 3/8" drive until it felt tight and took it for a spin. No drips, no leaks. The front differential drain plug faces straight down.
The rear plugs were torqued to 30ftlbs and the fronts were tightened with a 3/8" drive to snug.
Here if the fluid at 6,500 miles:
This is what the new fluid looks like: