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.
I have a couple of friends that use different lubes too. One uses "Marvel Mystery Oil" and the other uses cooking oil. Myself--I have a few AFX racing oil bottles and several bottles of the red Aurora oil. Probably enough to last me this lifetime, anyway.
Over the years, I've tried many things, but for the vintage cars, I keep coming back to the same thing........................light weight sowing machine oil, it looks like yellow water, but is thin enough to not create drag/friction and it's cheap!
I'm currently using Marvel Mystery oil; the pint I have should last a LOOOONG time... and AfxToo, the guys I race with have said the same thing about the bottom hole. I've thought about using something thicker there, but haven't gotten around to finding something to keep in my pit box...
in the holes on the bottom and through the top plate i use some teflon grease i picked up at radio shack works well and last a long time on my jl i use lubriplate grease for full size autos has teflon in it and is thick enough to keep the motor from shaking as badly as oil till i get bushings installed