Hello,
The handle and faceplate are only cosmetics, the valve body itself has a cartridge in it that turns water on and off. Sometimes a complete replacement is the order of the day to stop the leaking, if I knew a little more about faucet would help. Go to moen.com look up shower faucets and they have a breakdown ot schematics and should help you. Sometimes they will send a new cartridge if yours is a Moen.