I have a delta single handle faucet for my bath. There is a pushbutton in faceplate for shower, The unit is about 20 years old. The pushbutton will not stay in anymore and is spraying water from the button. I want to replace the control valve/diverter in wall but am unable to remove the faceplate. There are 2 screws in faceplate and one in handle. I thought faceplate would come off but it appears there is a threaded piece that covers ballvalve in handle that may have to come off first. I tried to remove this but it won't turn. I'm looking for advise on what holds faceplate on. Also is it possible to work from rear of faucet to replace diverter. I would have to cut out a piece of sheetrock or is it better to work from front where tile would have to be removed.