Chainsaws

I have a Poulan Pro PP4218AVX chain saw. Family 9PWES.0424CN/42cc:EM, SN/09125D401927-2:(10:54), Model PP4218AVX 802145. I purchased this saw from Lowe's sometime around the end of 2010. The gas cap has been very difficult to remove and replace since the middle of last year. I have replaced the cap and it now has the same problem. I see that others are having similar problems with theirs. Is this covered under warranty? As a side note I have friends that are having similar problems with plastic gas tanks on their motorcycles and attribute it to the ethanol in the fuel and the tank expanding. Could this be the problem here and do you have any suggestions on how to mitigate the expansion?