(Started writing this earlier, so there's some redundant material...)
Haven't had a chance to mention it until now, but I got the same reply from Italy. I did write them back and let them know their distributors (Areiete in particular) were telling their customers something different.
I'd swear the stems on my bike have O-rings on them, but it's been a decade, and I guess you forget stuff like that over time.
I do know the current stems are a different design than the older ones, so maybe mine do.
The EPDM rings seem to have established a decent track record for not causing trouble, which is good. The shelf life of EPDM is 5-10 years (less in service), so mine are quite clearly in need of replacement. That may be why Bridgeport recommends such frequent changes: "tire change" isn't a unit of time, and if it was, it would vary with every rider.
EPDM has fair resistance to compression setting, which is where it assumes the shape of whatever it's sealing over time. That's not necessarily a bad thing, because it often provides a better seal. Its big weak spot is that it doesn't get along with hydrocarbons (fuels, oils, etc.). We're certainly not dousing them in the stuff, but they do feature on our list of nasty substances found out in the air on the road.
If we were looking at regular O-ring replacement, I'd be going for a fluorine-based rubber called Viton that does fine around pretty much every substance you'll run into on a bike. It's better at resisting compression set, has a much higher maximum service temperature and the material has a 20+-year shelf life. Viton is three times more expensive than EPDM, but you'd be staring down about $7.00 (vs. EPDM at $2.50) for a bag of 25 that could be split with a friend and would last both of you 20 years.
I wasn't able to find any standard part that resembles what's on the newer Bridgeport stems, so I'm guessing they're custom and the path of least resistance is new stems. I think, based on how mine have performed, I'm going to replace them at the next tire change and at 7-year intervals thereafter. That'll more than cover valve cores, too.
--Mark
P.S.: Larry mentioned earlier that the bands for his spear guns deteriorated rather quickly. I did some poking around and found that many of them are made of latex, which is at the bottom of the longevity heap with natural rubber. Both have a shelf life of 3-5 years and don't tolerate the outdoors very long.