I don't adhere to the "thinner is better" rule when it comes to the bottom hole on pancake powered cars. The thinner oil wicks up into the motor and fouls the brushes and runs out the bottom and fouls the track. A heaver oil (red racing oil or ATF) or even a lightweight grease is not out of the question for the bottom hole, in my opinion. Overall I think that most people worry way too much about special oil formulations for slot cars. Just about any oil that doesn't react negatively with plastic should be a fine choice, including but not limited to sewing machine oil and the synthetic automotive oil. Just don't overdo it. If you clean your cars before you put them away and oil them carefully before you run them they should last a long time.