Regarding auto fuel, I have been running 92 premium ethanol free Mogas in my 912uls for its entire life of 750 hours/5.5 years, except for a very occasional x-country trip using 100LL. Nearly all my Mogas is purchased on-airport, but occasionally from an auto service station that sells it. I ALWAYS sump the 3 fuel sump drains during my preflights. In all these hours and years I have never even once found any water or dirt in these fuel samples. I hangar my plane in wet and humid Portland Oregon and it sits many times during the winter for several weeks with only 1/2 full or less tanks. This is just my own experience and yours may vary, but I have quit being worried about auto fuel and water condensation problems; however, I will continue to always sump my drains during every preflight.