SMC valves passing air through

I have some 1/2" 15mm SMC valves, they sat out in the elements since jan without being used, and recently i hooked them up and they work fine, but you can hear air leaking out of the dump valve, even when it's dumped, so i figure it's leaking through both valves and it drains the tank. I've cleaned them out, could it be a weak spring or something?