OK
-- here's where I (continue) bashing my head against the wall! YES -- you are most correct vis canned fuel -- I have been a lonnng-time user of Stihl Moto-Mix in my (all Stihl brand) chainsaws, pole saw, and blower. I add a wee bit (2.53 ml) of Stihl Ultra to each quart, too. A YouTuber -- Chickanic -- has posted several diatribes AGAINST using many pre-mixed canned fuels -- you can Google her channel and see the brands she particularly nixes. Being OCD re oil-mix I recently couldn't get an 039 going, and dealer advised scored piston.
I always warm saws up before use, let them cool down after, etc. How did this happen? (I mailed the saw to Corey C. in Oklahoma for rebuild...) But, many hours of research -- which even got me to this forum -- suggests a Red Armor mix to 40:1? The relatively short amount of money -- cost -- is nil, counting pennies when I'm running a $600.00 saw -- I'm both too old (I'm 75) and too poor to buy a new replacement... Mentioned as a possible failure cause by Stihl (their website) includes "stale fuel". Which might (???) have been a contributor to my 039 failure. Since -- shoud've done it in past -- I now label all my premix with date -- and any left after a couple of months gets poured into my pickup truck's fuel tank. I'm still seeking the "answer" to the perfect mix which will make my saws last