Ok how long are we storing the equipment? E free with any type of decent stabilizer will easily last a year with out worry of gum or varnish build up. If its beyond that it doesnt much matter what you used as it will be evaporated out of the system by then. And I've not seen any manufacturers that want any engine stored beyond that with out it being ran. So for the sake of argument let's keep storage period to 12 to 14 months, which I think is a bit generous for what were talking about.
Now on to rubber parts. They will degrade with time, just as much with use. I have some nos carb kits I got from a friend, for old mac's and tillotson carbs that are basically junk. They've never been used or out of the package for that matter. The diaphragms are basically rock hard. Theres really no way to prevent it, the fuel will eventually harden them as well. Doesnt matter the fuel or treatment, just a fact of life. Best case if running no ethonal laced fuel they will last longer, but nothing is impervious to age and wear. I do wish walbro would release their spiral diaphram for more of their carbs, and teflon gaskets for the pump side. That has alleviated a lot of the issues we typically see in the small power equipment. Along ad your running good fuel, there is no affect on the diaphragms.
At any rate, I think were getting a bit deep, if not having a good discussion on what I would term extreme long storage.
Cheers