Curious what would be the recommended oil fill for a Buick 401 Nailhead engine with 98k miles. I am 99.9% certain that internally it is untouched original from 1965 in my knowledge of the car, and there is nothing to indicate that it has had any work done to it. In researching I've pretty much gone in circles between Rotella T4, Super Tech Heavy Duty Diesel, Valvoline VR1, Brad Penn, Mobil 1, a good amount of zinc is important, zinc doesn't matter at this mileage, any oil has enough zinc to be sufficient, do use zinc additives, don't use zinc additives, and so on. Most of the forum posts on this topic are getting older at this point (mostly late 2000's-early 2010's) so some of the info given is sometimes no longer relevant or accurate. The car isn't driven in winter and only will get 3-4k miles a year at the very most, being driven on nice days. I've figured sticking to conventional is best as it doesn't have any major leaks at this point so I'd rather not dump synthetic in and find out several leaks have now opened up. My initial plan was Rotella T4 as that always seems to be the go to with all the "vitamins and minerals" for an old engine but then after reading that it was and now isn't gas engine rated (I think, haven't had a chance to look at a bottle), I've been reconsidering as a carbed engine is going to have a lot more gas contamination in the oil, etc. I don't plan on doing any engine work as it seems healthy at this point so keeping in it's current condition would be great.