Not trying to start a "best oil war", just trying to get ACCURATE information. I have a V8-270 C-B, cat motor. I usually just run the recommended Volvo 10w40 oil, but it is getting extremely hard to find in my area and very pricey. The manual recommends any high quality oil 5w30 or higher (10w30, 10w40, 15w50, ect.). I have thought about using Mobil 1 15w50, as I can get it easily, but have read it has a high Zinc level. I have read that oils with high zinc levels should not be used in Cat equipped motors. Is this true? Also, should I just pick a good quality 10w30 synthetic and call it a day? My other option would be to get a good quality synthetic 10w40 in a "High Mileage" oil, since that viscosity seems to be only in "High Mileage" for synthetic oil. Will the seal conditioners cause problems now or later if I go that route? I know I am probably overthinking this, but any advise is appreciated.........Thanks