I have rebuilt of a few of the original style double action pumps and have always used new neoprene diaphragms and new valves that contain good rubber seals in them. There are still quite a few of the "new" fuel pumps being sold over the counter that do not have good diaphragms and parts to handle modern fuel. Ethanol is always a big concern, but there are other additives to contend with too.
Can't remember right off hand, but there are only a couple of suppliers for those neoprene diaphragms... those old fuel pumps aren't too hard to take apart and put back together. You would be surprised what you could do.
Daniel JessupLancaster, California
aka "The Hot Rod Reverend" 
check out the 1955 Ford Fairlane build at www.hotrodreverend.com