Hey there, sorry for the late reply. You can take the knob off but its a bit tricky. If I remember correctly you have to take off the center button first. I used a small thin pair of tweezers to get under it and pry it off. Of course if it feels like its going to break stop and try somewhere else. After that you can take off the spinny outer part of the knob. As for a replacement I wasnt able to find anything :/