You really don't need to do anything if you don't mind that the letters don't line up. It won't affect the operation. Almost all automags experience this to some degree because there is a tiny bit of wiggle room in the z-lock slot. Some just have a bit more movement than others. I suspect it is more the rail than the valve, that is causing it. You could tighten up the z-lock slot a bit with some filler (JB weld or similar) on the right side of the slot to prevent movement in the rail. That way you wouldn't have to do anything to the valve itself.
Except for the Automag in front, its usually the man behind the equipment that counts.