If choosing an aircraft oil, go for oil for turbine, not piston engines, the latter are no better than automotive engine oils as they need to be chemically active to deal with combustion products. The additive packages in oils for piston engines are rather nasty. Avoid skin contact even with fresh, new oil.
Transformer oil is a good choice, but that opens the PCBs can of worms, so let's dodge that one. Transformer oil which you know is PCB free is good.
Medicinal/feed stuff can have some water content. but you should be able to drive that off by heating it for a while.
Aviation stuff has to be water-free or you are in trouble.
More people have access to pharmacists than to aeroshell. The tanker drivers topping-off your private jet, do stock it on their truck and add it to the bill
David