Stew----Normally 5 years in service. But understand, we assume the hose is submerged in fuel, and we dont know the additives in the fuel. But we do know that whatever those additives are, they deteriorate the liners. In Larry's case, it made the hose very stiff, so it wasnt going to flop.
Teflon would be fabulous because the liner doesnt deteriorate, BUT its pretty stiff as is, and doesnt flop well. WE messed with a live swivel fitting several years ago, and it worked, but wasnt cost effective.
So right now the best solution I can say is to change the flop tube every couple of years. Yeah, I know, its a pain to reseal the tank. but until a better alternative comes up, I guess thats what has to happen.
Tom