There are some great oils on the market intended for outboard use that are NOT a good choice for small air motors.... so don't use oils with TC-W3 seal. Air cooled motors operate at higher temps than outboards, so they use a lighter oil base which won't be conducive to long bearing life at those higher temps. I've had good luck with Stihl 2 stroke oil and it's easy to find. If you want to spend a little more.... Klotz is a good oil to use and they make several varieties. Make sure to get the one for air cooled use. If you use fuel with higher alcohol content or other funny stuff then the bean castor oil would be a good choice....smells good too.
I've know a couple of racers that swear by Klotz: