The temperature control knob is hard to move on my Delta Monitor 1700 series shower handle. I've taken the cover off the knob and I can see that there is a warning not to tighten the center screw too tight. That was not the problem. In fact, that screw had gotten so loose that the knob was about to come off. Would it work to spray some WD-40 into the area? Is there some other way to make the knob easier to move back and forth? My motivation for asking about this is that my wife finds it particularly difficult to adjust the water temperature.