wintersun wrote:
pay twice as much for an oil change which I have to have done twice as often
Other than everything else you said about your Duramax diesel, I don't understand the "have done twice as often" part.
My oil changes are recommended every 7,500 miles, or 15,000 miles if I was doing continuous over-the-road hauling.
I change oil every 7,500 miles. My dealer and I made a deal for lifetime oil changes and tire rotation for less than I can purchase the filters and oil from the local parts or discount department store.