I just serviced the fuel system on a recently acquired Hitachi Ex 120-3 and in doing so changed the fuel filter, cleaned the screen and emptied the fuel separator. The prior owner had an inline electric pump that I activated to prime the system. Days later the fuel separator was found leaking so I replaced it with a new one and then primed the machine again. After a couple days use (2-3 hours each day) I noticed the exhaust was spitting black residue - a lot of it. The machine has no loss of power and the turbo seems to work fine. I checked the oil and noticed it appear thin And not as black as it should be. The machine has about 20 hours since its last oil change. Although the level was at the full mark, when I pulled the dipstick, there was oil residue in a couple of places higher…that I thought was odd. Could I have over-primed the fuel system and somehow contaminated the oil? The turbo shows no obvious signs of leaking. The machine has 5600 hours. It is an Isuzu engine. If contaminated oil, is this simply change the oil and filter and see if it still spits residue or is there something else I should look at. I checked the oil pressure exhaust that typically comes from the valve cover but it did not show any obvious signs of being over pressurized. None of the turbo lines appear kinked and the air filter was recently replaced.