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Spraying the valve stem with WD40 won't work because the packing around the stem that keeps the water from leaking out will stop the WD40 from going where you need it. You'll probably need to replace the valves. You could try turning the water off then back off the hex/bonnet nut behind the handle and remove the stem then clean and grease the threads on the stem but there's a good chance the valve will leak or fail when you put it back together so you have to be prepared to replace it going in.
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