Maybe the Ethanol but I have seen that on many older carbs in Canada and we don't have corn juice in the gas most times. I can almost bet that's what I'd find in the little chain saw that's getting hard to start, not CVs but diaphragms and looking like that all too common.
Interesting anyway, I have a set of CVs from an american bike here I don't think have ever been opened. If I can just unseize the screws after 25 years of corrosion, I'll look.
Just to say that things like that happened well before the corn juice in the gasoline.....and the Internet. Maybe they happen faster now, that I wouldn't know. What I do know is that my 90 R100GS, Canadian specs never liked American gas in general even 20 years ago before the corn juice.Pinged like crazy and yes had to replace the diaphragms at one point, that's just a wear part to some of us.
I'll add a diaphragm to the carb parts/fuel lines in my straight Ethanol test jar. Haven't looked at that for a couple months.