I have/use 8 trimmers/chainsaws/blower that use 2 cycle mix. I have been using a 50:1 mix of ethanol free premium and Pro-Mix Premium Synthetic Blend 2 cycle oil in everything for years. Some of the equipment manuals specify a 40:1 mix. Am I doing any long term harm using 50:1 in everything? Most equipment is 1970's - 1990's with one new trimmer (50:1 spec).