Synthetic Mobil 1 high mileage - 2003 4.3 litre 160k miles I have used Mobil 1 high mileage 5W30 for years. With the Mobil one high mileage filter. Change oil & filter every 6k miles. I changed the valve cover gaskets yesterday and took pics of the rockers and related .. I was very surprised to see how clean everything was. See attached pics.. Wanted to share my findings.