ORIGINAL: Carosel43
I do not drain the oil at the end of the day I wait until the next flying session. My logic is why drain out all the oil before you store it? is it not better to keep that oil in there and drain it out a week later (when next flown) and replace it with new oil? anyway, my engine is not rusty...that's about the only thing that's not wrong with it!
Any unburnt methanol in the oil is hygroscopic, so the moisture it attracts will promote rust, and any partially burnt fuel residue will be acidic, so its not really a great idea to leave that hanging around in there unneccessarily. I believe 'recommended practise' is to flush with Kero then add ARO and try to distribute it to all parts of the engine.