Is the Pennzoil 25W50WT available off the shelf or do you need to order it from a part store? What's the cost per Quart? Many people talk about Zinc content and I see normal commercial oils recommended, do they have a high enough Zinc content? Several people run diesel oil and have great luck, some worry the oil foams so that makes me stay away from diesel oil in my engine. I change my oil once per year due to working in Kuwait so my drive miles are very small per year. Thanks for your comments.