I've noticed a number of machines here that the oil turned black. I think what happens is the machine runs "Dry" once or twice. A little bit of "debris" is formed from the joints rubbing on each other and when the machine is oiled next again, it's the mixing of the oil and the debris that makes it turn black. It's especially bad where the grease is used on the gears if the gears ran dry and someone was over enthusiastic with the next greasing. I'll look for the picture of my 401 before I cleaned it up. There was black stuff flung everywhere, it was nasty.