Sean,
I agree to a point about your saying different oils should be verified, but one oil that was not checked was olive oil!
You might be surprised to find that it allows the platter to turn even longer than the motor oil.
BTW, longer turning time does not indicate that the lubrication is better, just that viscosity of the lubricant is lower therefore allowing more shearing of the lubricant itself which puts less drag on revolving spindle.
In fact too low a viscosity could be bad, since the lubricant barrier formed between the metal parts would break down and then we would have metal touching metal and increased wear. The platter, however, might turn for much longer, since the actual friction of metal to metal (sometimes ceramic) surfaces might be lower than with the lubricant between them.
Motor oils are for much harder lubricating conditions than a "babbit" bearing, which a turntable bearing is basically. That is why I said that motor oil is over kill. For lubricating a simple spindle, a light machine oil is all that is needed and while I might have been facetious in saying that olive oil would be just as good, I am sure that that is true! Try it, you might like it! (Pun intended).
Salut, Bob P.
PS. As a professional Chemical Engineer and having managed synthetic lubricant plants for several years, I am quite sure of my views on the subject of lubricants and their applications.