In the course of hunting for examples of 100% ethanol-powered piston engines, I found the Embraer EMB 202 from Brazil that is modifiable to be that way.
But the article also says "The alcohol fuelled Ipanema engine also has 20% lower maintenance and operational costs." (no citation there, howerver.)
I also found this PDF that says similar things:
Avgas is slightly cheaper on a per-kilometre basis than ethanol, but the lower maintenance costs associated with the use of ethanol ultimately make it a cheaper fuel option for pilots.
Why is this? What exactly are the modifications made to normal engines that somehow reduces operation costs? And why aren't these modifications made to normal engines that just keep using avgas?
(Please: let's not get into an off-topic argument about whether ethanol should/will replace petrol products. I already know avgas is about 40 MJ/kg and ethanol more like 28. This question is not about that and I hope it doesn't become another casualty in that flame war.)