If the shaft is broken or the contacts of the shaft, you could order any pot from the same series and remove the shaft for use with your existing pot. If it's not a broken shaft, I would carefully take it apart and determine what exactly the problem is. Sometimes you can give the contacts a little tweak and make it work again. If the wafer itself is bad, I guess plan B is in order. Of course it's best to just replace a bad pot, but sometimes desperate times call for desperate measures.