Pre 1990 and especially pre 1980 fuel systems were NOT deigned to run a high concentration of ethanol. All sorts of fall out. Modern engines and cars, absolutely. Is ethanol the "devil" that has everything up to and including the Black Plague associated with it? NO!
However, fuel delivery components designed and installed prior to the late 80's and early 90's DO NOT LIKE A DIET OF ETHANOL. Can the composite gaskets, o-rings, diaphrams, etc. be upgraded to modern materials? Absolutely. Do I have modern rebuilt kits for my F-12 fuel pumps? You betcha. Did my original 1949 KB5 Carter carb start whizzin' all over the place after I ran it for a few hours on E85? Yup. Have I seen complete NOS fuel pump failures 100% of the time? yup. is it likely that some of those failures can be attributed to dry rot? Yup. When I open them up, the diaphrams are the consistency of rubber cement? Hardly dry rot.
Believe as you will. I have absolutely no issues with E85. Upgrade your fuel delivery components to run on it. If you vehicle or tractor or whatever is older than the 1980's on, do yourself a favor. replace plastic and rubber type seals and diaphrams before running on E85.