I am deciding what to use in my freshly rebuilt 20 year old LS1. The Castrol 5W30 C3 has a good list of standards, but it's supposedly meant for diesels. I can't find a 5W30 with better "specs" on paper, except maybe Mobil 1 ESP (is that right?) which only comes in quarts so it's ridiculously expensive. Plus Walmart carries it. I don't want to use an Xw40, since that's what I was using before the rebuild and it's slightly possible that could be the cause of some cylinder wear it had (there's no other likely explanation), and also the original owner's manual specifically says not to use a 40 weight. So looking for opinions on whether the Castrol C3 would be a good choice.