Dry graphite lubricant works best. I used to use the stuff for pinewood derby cars; you can find it at many hobby shops. It doesn't attract dirt like greases or oils, and you can use it for lots of things (rear axle, gears, suspension..)
The funny thing is that I've seen baby powder recommended on several web sites in case you can't find dry graphite lube. Looks like you ran across a good thing by accident
