The underlying chemistry of materials compatibility can be a bit mind boggling - but in the end it comes down to permeability: if a fuel or solvent can permeate the material (pump diaphragm, fuel line, gasket, glove) it will eventually break it down. Add pressure (like in fuel injection) and even historically proven materials can begin to fail.
The folks over at
efunda present o-ring material compatibility data in tabular form making for easy comparison. Take natural rubber - it is rated 4 for use with ethanol; but rated 1 for use with gasoline - making it poor choice for blended fuel.
As for the compatibility of ethanol with metals - it's really not the ethanol that is the problem - it is the fact that (like brake fluid) ethanol is hygroscopic. Both literally absorb water from the air. In brake systems the key is to keep the air out as much as possible - and to flush the system regularly to discard the water logged fluid before it can rust components.
The same is true with Ethanol (end even more so Methanol) based fuels. This article over at
The Shop Mag discuss the problem of corrosion in parked vehicles.
Seems the more a vintage vehicle is driven the better it will tolerate ethanol based fuels. But if one must park it - flush it.
