diverter
That is not always a bad thing. In the "old days" diverters, (the ones on the tub spout), were intended to leak so that the diverter would reset to the tub side after the shower was used. That prevented the next user from getting a blast of cold water when the faucet was turned on. But, stem type diverters are different. The main difference is that they are usually a double seated stem, and if the stem does not fit into the valve body exactly, then water is able to penetrate around the stem, and no amount of tightening will stop it.