straight 30? I wouldn't use 10w40 unless it was very cold. You need the viscosity for some oil to stay on the cam when not in use. I used older Shell Rimula X & Castrol Rx Super of CJ-4 Spec, 15w40, but drove it every day. These higher spec diesel oils also have additives that help with acid build up in your oil if you don't use PCV. They last A LOT longer too, with stock B18, B20, B230 I would use a double size filter, change the filter at 5000 and the oil at 10,000 miles. Even my racey engines, I would go 2500/5000.