I just purchased a house that was built in 1962. Water was dripping out of the shower head in the master bath so I first started by replacing the little rubber gaskets at the back of the stem - it still dripped. Because the stems were completely plastic and appeared brittle, I replaced them with brass ones. Now the dripping has stopped, but it takes all my strength to turn on and off the hot water. I'm sure that I did something wrong, but I don't know what. Any suggestions?