[Stinkyfinger]

The metal shavings are normal the pitch black color is not
I've changed the original diff oil on previous vehicles at 70,000 miles it had shavings in it, but it still looked like new oil. I have never seen diff oil turn that black. I thought maybe it was a special oil for break in, but the front diff and transfer oil looked brand new.
On a side note I gained 1.4 mpg switching to synthetic. I switched to royal purple about 5 months ago and I am still averaging 1.4 mpg more. The large gain might be because I'm all wheel drive(more moving parts), but you can never go wrong switching to synthetic.