[McGruff]

Ethanol-blends deteriorate almost the moment they are pumped, and can break down in the fuel tank causing:
Rust
Corrosion
Gum/Varnish Build-up

And the longer these blended fuels sit in the fuel tank, the more damage they can do, resulting in:

Starting issues
Rough running
Severe engine damage

https://www.briggsandstratton.com/us/en/shop/why-genuine-parts/fuel-treatment

I use their additive in the gaslonine I store.

[VRWCarea51]

Seafoam!

[Marko413]

Ethanol-blends deteriorate almost the moment they are pumped, and can break down in the fuel tank causing: Rust Corrosion Gum/Varnish Build-up And the longer these blended fuels sit in the fuel tank, the more damage they can do, resulting in: Starting issues Rough running Severe engine damage https://www.briggsandstratton.com/us/en/shop/why-genuine-parts/fuel-treatment I use their additive in the gaslonine I store.

This exactly. I started hearing early on from commercial fisherman and folks that run summer camps how the ethanol deteriorates so quickly and eats up the seals on the engines.