My 2 cents worth; Look for a super clean floor, and a clean shop. Most don't think so, but the inside of an engine IS very clean. One spec of grit in an engine and it is done. That's the purpose of the oil filter, to catch the dirt. And the reason you should always change the filter with the oil. Good mechanics have a clean shop & floor. Incidently, in the past year I have learned of a benefit to Mobil-1. It doesn't burn as easily as other non-synth oils, so it should lubricate better on hot summer days. Jim Ussailis jim at nationalwireless.com