max2cam
ArboristSite Guru
I don't know anything about Citgo oils and I've never used them. If you're milling though, I think a full-synthetic is in order. I've been using Silkolene for milling.
You are probably almost certainly right. I'll have to do some research over on the milling forum and see what oil guys are using. Maybe I've been too lax, certainly my saw thinks so...