Gernby

You can't use any sort of hard washer, since you can't tighten it down with a wrench. It would have to be a soft washer (like the one provided by Fumoto).

Nobody

I examined a friends valve purchased for an Evo...how long will the non metallic washer last? In addition to the low ft/lbs the sucker should be torqued on with I'd be worried that over time the rubber washer will dry, crack, shrink and allow the valve to back out (talk about a quick oil change!). Am I just too paranoid?

MacGyver

Been running my valve for over two years now without issue. It has never backed out an inch or leaked a drop.