I have a Price Phister shower water mixer. After about 10 years the screw that holds the hot/cold on/off knob to the shaft of the water mixer seems to have stripped out. I suspect the metal screw that holds it together is going into a plastic fitting that has fatiged over time and is stripped out . Any suggestions for an easy fix or is it the rip out and replace drill?

If you are sure that the screw goes into plastic try one drop of Crazy glue. Push the screw into the hole with a slight twist and leave for several hours.

Or use a toothpick in the screw hole.