I bought a Softail with EFI last month that had been sitting for 4 years. Owner denied it, but I think the fuel was 4 years old, too since it hadn't been registered since 2018.
It ran a little rough, so I added half a can of SeaFoam to 'clean-things-out'. Now, about 2 weeks later & having added another half can to a fresh tank, my Fuel Quick Disconnect began leaking.
I got the 'Fuel Tool" brand rebuild tool (so easy) and their valve, spring & O-rings and set to rebuilding the check valve. While removing the lower O-ring, the valve & spring just fell out. Seems the top O-ring was non-existent. I'd recently put a few hundred miles on it so I was really shocked. It is always the bottom O-ring that so commonly gives out.
Seems the top O-ring was completely dissolved VERY recently. I'm quite certain most everything on the bike (2005) is OEM, which is 17 yrs old.

I've read the OEM O-rings of pre-2012 do not hold up to ethanol, so I'm thinking the SeaFoam overdose must have really trashed them.
I'm told the new O-rings should be made of 'Vitol' in order to resist chemicals, which I'm now using.
With 20/20 hindsight, I should have just drained the old fuel, but I've used SeaFoam in bikes, tractors, vehicles for decades w/o problems.
Sure looks like I 'screwed-the-pooch' on this one. Can't think of any other explanation. Just dumb luck it happened in my garage & not 75 miles away.
Anyone else have this problem (and willing to admit to it) ?

 

In 2015 I bought a 1996 BMW R1100GS with 4K miles on it. When I removed the fuel pump from the gas tank to change the fuel filter, I noticed that the plastic fuel pump intake filter/sock had completely dissolved. The autopsy on the original fuel filter revealed nothing interesting. The bike ran just a bit rough but ran better after a couple tanks full of gas treated with fuel injector cleaner. BMW now sells small bottles of fuel injector cleaner but I use Techron in my bikes once a year, and treat the gas with StaBil when they're stored for winter.

 

I don’t think the O-ring damage was caused directly by the SeaFoam, but rather just exposed.

My theory is they were already damaged and dried out from the old ethanol gas, and ready to crumble. Then the SeaFoam took them the rest of the way out. And maybe is was a bit too much SeaFoam. Being a big believer in SeaFoam myself I’ll have to scrounge up some old O-rings to test it on.

 

The old, rotten gas and age dries your petcock o-ring. I swear, it's the first one to go on old bikes.
I just had to change on on my 20 year old dirt bike that sat for 3 years.

Seafoam should not have been the culprit, and I too am a fan. I think you did just find with your method.

 

My 03 springer with 12 thousand miles started leaking from the top O ring. Yours was probably already dried out and the vibration and sea foam to some extent helped things along.

 

The crud "helped" with the seal
The Seafoam dislodged the crud

 

Allowing fuel to remain in the bike stored for years will cause considerable problems. No additives can correct that.
The fuel system components must be drained and flushed with solvents formulated to remove the deposits. Non-Metal parts
that have degraded need replacement.