I can't get ethanol free gasoline, well anywhere close and I'm not about to make a special trip for it. I use the 93 octane, with ethanol, for years now, in a MS 390. I do treat that gasoline with Startron. I use Stihl oil in the fuel, precisely with both the oil and the fuel, I flush the little bottle to get all the oil out and make sure the fuel is just below the 1 gallon mark.
I just completely disassembled this saw and re-assembled it. Somewhere in the last 4 years I did replace its original fuel line, which did crack in several places. As I was putting the saw back together, I checked all the rubber parts thoroughly, held up to the sun, checked for holes, cracks etc., nothing, so I reused all except the fuel line, replaced that, but the one I took out was fine, saved it as a spare. So it seems the fuel I use does not seem to create any problems in that span of time, the saw does sit for periods of time, no issues if it does, always fires up, before the tear down, it sat since May, 4 months later it fired up as if it was used the day before.
I realize that the fuel storage containers, can suck in at times, and you may get moisture from the air, not sure how that works with ethanol, being alcohol, it traps it ??? So maybe there is something to treating the fuel and using a quality airtight container? Stihl offers some kind of alleged non spill container that is rumored to perform very well. You have the metal safety can manufacturers like eagle and the other one, just something to consider.
The one thing that stood out when I looked the engine over with this saw was that it was well lubed, I could see no significant wear on the cylinder wall or piston. I've had it since '02, intermittent use throughout the year, more use spring and fall for firewood, part of the reason little to no appreciable wear, that and the fuel mixture I use, had to play role in that.
It does start easily the 2 pulls on full choke, fires, then click the lever up, one pull and its running.
The only issue with this saw and I still cannot figure out what causes it, having taken it completely apart is that it shuts off once in awhile, seems fuel related, as I've feathered or pumped the trigger throttle to keep it going, which sometimes worked. Earlier this week, was felling an elm, made the face cut, stalled, so I set it down, waited, friend stopped by actually, happened to be in the neighborhood walked down to where I was working, in a little while, it fired right up and ran fine, ethanol/moisture ??? It has me baffled, I thought well maybe it the coil and plug wire, the end connector is a stab in type, and I actually pulled that apart and reset that end on the wire to make sure it had good contact. Appears to be fuel related, but at this point I have no idea, otherwise the saw does run great and gets the work done most importantly.