Product review (5 stars): There are some good videos on Youtube to dismantle
This pot wore off on my 15955 machine. You can tell when you have erratic speed control. For example, as you move the speed from 0 through 2 it will surge up much higher, even temporarily.  That is a symptom of this component being worn out.  There are some good videos on Youtube to dismantle.  Repair was very easy, but you need a 10cm long (or longer) 2mm allen wrench.