Blower Motor Fan Control

My control for the blower motor has stopped working. It is stuck on second notch below high (good thing it stuck there up here in Siberia). I notice a few weeks ago, it kind of binded at medium moving from high to low. I took it all out last night, but can't seem to figure out what is not working. Everything is turning everything. I could not get inside the part where the knob slides on, but that feels similar to the other 2. Any one experience this or know the fix?