#1, it was common enough in the 1980s that GM specifically stated in their owner's manuals (and issued a TSB) allowing it's use..
#2, the OP's bike is 1998 model and I can assure you that ethanol gas was used back then to comply with the oxygenated fuel mandate in non-attainment areas, particularly in the midwest region of the USA (Indiana, Illinois, Wisconsin, Minnesota, Iowa, those "corn belt" states). EDIT: And some of these states seemed to have laws "encouraging" the use of Ethanol instead of MTBE, prior to the MTBE ban....
My original point is that ethanol fuel has been available for at least 40 years. It would be reasonable to expect a 1998 model bike to be able to run on 10% ethanol fuel and for that to not cause damage to the fuel system.
Hell, I would expect it of a 1988 model bike.
One thing I would also expect is that today's ethanol gas is better than what we had 40 years ago. Technology marches on, and gasoline is no exception.
Referencing manuals instead of actual people who were alive and driving in the 1980s is a strategy that tells me you were either not there or too young to remember. I owned 1980s GM vehicles, I read the manuals (because there was no Internet in those days and life was boring in small town Oregon) and I distinctly remember there were references to Gasohol fuels in the manual. That does not mean actual pump regular unleaded contained ethanol. The pumps containing Gasohol were clearly labeled and you had to make a conscious decision to dispense it in your tank. I knew people who used it constantly and liked it, but most people were afraid of it.
When oil prices crashed in 1986, gasohol started disappearing and by the 90s I never saw it anymore.
In actual inflation adjusted terms, gasoline in 1979/1980 was the most expensive it had ever been, before or since. The idea of gasohol caught on because it was cheaper and also produced less smog, which was a BIG issue in those days for some cities. It was NOT used as an anti-knock additive, MTBE was widely used and the pumps were labeled as containing it.