I have a question I haven't been able to find the answer to. I have a 2009 JD 4520 Compact utility tractor. I changed the oil around 40 hours ago. Here's the question: When I check the oil, the dipstick shows clean oil on it. I expected it to be black, but it never is. Last week I actually drained a little of the oil as it was reading a touch high on the dipstick since when I changed it, and it was as black as coal, but the oil on the dipstick is still clear and yellow. What's going on?