We have a friend that tests the crap out of ethanol fuels.
When you re-still 91 octane (which came out of the pump
at a busy gas station and was found to be 17 ish % ethanol),
and has only sat 3 weeks, you would sh!t yourself at the
crazed black yellow slime varnish that is left over from all
the additives and ethanol.
Same test with 91 octane non-ethanol(unleaded gas) sitting
for the same 3 week test, re-stilled got him no slime
but just a tad yellow and very very faint varnish smell.
I know what I'll be putting in all my engines.