I guess all those years back doing this just sold me on the oil and the engineer I took 3 weeks of class with who worked for Mobil didn't hurt either. I have never looked back. Les he never changed the oil in his vette until 10k,,,, Some of my analysis recommended oil changes up to 25K in the vette. Not sure they make recommended oil change times any more, but it proved the oil was still good and doing its job. Sending off a sample is good when you think you may have a problem. Like looking for antifreeze in the oil.....