The Forestry Forum

I understand that this is old news, but I didn't know about it.

http://www.stihlusa.com/information/recalls/toolless-fuel-cap/

Just read the recall at the link provided and I notice that it doesn't seem to pertain to any chainsaw products..
It sounds as though ethanol is the problem, making them swell until they won't seat properly.  I had a similar problem on an old Craftsman / Poulan saw where the fuel cap swelled until it was almost impossible to remove. I replaced the cap and stopped using gas with any ethanol and the problem stopped.  I also noticed that if the cap was dried out for several days it would shrink again...

I don't know so much if it swells them more so it makes them hard .

So you have a choice here .8 bucks for a cap or 29 cents for an o-ring .If you Google it you can find the size .It seems to me something like M3.5 by 20 or 25 .Flea bay sells them in generic sizes fairly cheap or I suppose the purists among us could buy a genuine, bona fide, real McCoy  Stihl o-ring if it makes you feel better . ;D