I have a problem in my shower. When the faucet is switched so that water should be coming out the shower head, a great deal of water still comes out the bath spout instead. What is more, when the hot water is turned up, the water coming out the bath spout gets very hot but the shower head water will only come out luke warm.

The shower has three knobs: the left and right turn toward the center for hot and cold, respectively. The middle one is the diverter: water flows to the bath faucet when pointing down, and to the shower head when pointing up. It turns counter-clockwise, and should stop turning when pointing straight up, but over time it has been going further and further to the left, while the water has been coming out the bath faucet more and more.

The brand is Price Pfister, and these are the original fixtures in a 16-year-old house. They're also in the bathroom that three boys grew up in, so they have not exactly been well-preserved over the years.