Took my 2.8 to the dealer for my 2nd oil change. After an 8 mile trip home I garaged it and checked the oil level. The oil was pitch black, obviously having not been changed. The tech was half way sharp as he wiped around the oil fill plug and filter making it look a though he changed it. The dealership manager confronted the tech who swears he changed both oil and filter and that the black color of the oil is typical of a diesel. Having driven diesels for some years I told them diesel oil does get black---but not in 8 miles of driving. Why when I had my first oil change and drove home and checked it was the oil clean --- shrugged shoulders. Bottom line is dealer took a sample and says he'll send it out for analysis, he says you say it wasn't changed and my tech who is well respected says he did. Is it possible for an analysis to determine how old the oil is, or as I suspect is it just going to reveal metal fragments and contaminates. Is there anything I should request the analysis look for that could prove its oil with 7ks of miles on it not 8 miles. Thanks!