My 15 year old son bought his Charger from a guy who told him it was "due for an oil change". When we did that last night the oil was pretty dirty looking, but what concerned me was the sludge on the old oil filter. The strange thing was that it was all on the outside of the rubber gasket. The pic doesn't seem to show the amount that was there. I wish I would have pulled an oil sample, but didnt. Any thoughts?