This is the first time I've heard of one of the redesigned knobs slipping. Are you sure it's installed correctly? Friction with the O ring actually improves the hotter the player gets.

I've noticed that sometimes the O ring is pushed onto the shaft first, and then the knob on second - this won't usually work. All that happens is the O ring gets pushed to the bottom of the shaft, and interferes with it turning smoothly. Instead, the O ring must be fitted inside the knob and the entire assembly pushed onto the shaft.

Otherwise, maybe you have a faulty knob or encoder?

Rob