Ethanol absorbs water which doesn’t always play nicely with seals and fuel lines, or at least that’s the commonly held belief.

That’s an issue if you’re running E100. Gas+ethanol blends will dramatically reduce ethanol’s hygroscopicity.

But if water is getting into your fuel (focus on fixing that, not your fuel choice), isn’t it better if the ethanol can carry it through the engine instead of just accumulating as a separate layer?

Nothing scientific but on motorcycle forums I used to frequent people often blamed E15 for seals swelling up and no longer working. I can’t say if that’s the cause but I did have a face gasket between the fill neck and tank expand. After sitting out for a few days it shrunk back to its original shape.

How old are the motorbikes though? I could see it being an issue on bikes built before >=e10 became nearly unavoidable.

I wish my gaskets would swell a bit. All of my auto seal/gasket problems were on the intake manifold or oil system interfaces.

Here in the US, there are a lot of really old motorcycles on the road, compared to other vehicles. As they’re mostly pleasure vehicles.