[marlinspike]

Any brand of mineral oil is not the same. They vary VERY widely (I'd even go so far as to say the differences between the various conventional oils is greater than the differences between the various synthetics, but this is going by memory, not looking up the charts so don't call me on this small point). Exxon believe it or not is a pretty good one, Quaker State put out total junk for a long while, supposedly they reformulated but I don't know about that. Mobil was typically good, but ever since they had a bad batch of oil get out I stay away from their conventional oils. Shell is ok, Castrol GTX is better at lubricating, but it sludges. Valvoline is supposed to be not as good as GTX by the specs, but I've had better luck with it.