I'm going to take a wild guess here and say that as far as destruction of gaskets are concerned on early engines such as my 235 that I should not have a problem because the gaskets are cork except for valve and rear crank seals,and not a synthetic. However, your mentioning of requiring the use of synthetic oil, I wonder if that's really good for older engines.When you or anybody else runs E85, I'd like to read about the results.

Drew
Mid-Atlantic Chapter