BLACK SPOTS RESOLVED!!!!
Hi Gang,
I had the same problem and found the answer on another thread. The problem was in the braided lines connecting the hot water heater to the water line. The inside is black rubber and when they get old the insides peel away and release into the water system. I just replaced my hoses and cut one of the old ones opened and the black oily stuff was inside and came off in my finger.

Hope this helps!