My good friend has an 01' Silverado HD with a Duramax. He has 200,000 miles on it, runs Pennzoil LL 15W40 on a 5,000 OCI, the oil comes out about as clean as it goes in, and uses little if any. He could not be happier with the truck. Today on the job, he ran into some supposed diesel "expert guru" that proceeded to tell him that Long Life was a "light duty oil, the worst possible thing he use, and the only thing that kept the engine from blowing up already was the short OCI. The "expert" said that Rotella was only marginally better, Valvolene was worse, an the only thing to use was Chevron. He then ridiculed my friends short OCI as a waste, that he should be using synthetic blend, ("don't use full synthetic") and then ripped him for changing his fuel filter at 10,000 mile intervals, despite the fact that I get the filters for him at ultra low fleet discount prices, and the D-Max is known for injector problems. I did my best to reassure my buddy, but I thought maybe some of you could help refute some of the "expert's claims. Thanks if you can help.