Here is my solution to try first.
I cut a piece of neoprene rubber about 1/16" thick, reinstalled the valve which presses the rubber against the hole to seal it when you put the cover back on. The OEM arrangement uses this method to hold the valve against the cork seal. This should work the same way ... except no hole to allow the passage of air whether the valve is open or not.
Course this only works if you have the original valve.
