UK: Trafficmaster playing up

Got a 2000 E38 with trafficmaster/sat nav (not widescreen). Last few days, the control knob used to navigate the trafficmaster map has
progressively become uncontrollable - seems like it believes it is being pressed in when it isn't, etc etc. I pulled the switch panel out and found a unit that the switch leads to. Anyone know if I can get this part and replace it easily?
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