the fluid that came out of my rear differential looked a big like dark gray/black sludge. is it supposed to look like that? the front differential looked like oil when it drained, it had a bit of the sludge on the drain plug, but the fluid that came out was clear.
just refill it with the new fluid? (mobil 1 gear oil)
08 4x4, 16,000 miles, 1st change