Reply to VCI 100 Right Jog will only read forward

Hi all,
bought a VCI this week from Ebay with a known fault. The seller informed me that the right jog would only read forward and when trying to drag back this also read as forward. I thought i would open up the right jog and find a mass of dust within the encoder and have it back on track in no time with a view to modding it. However i have cleaned the encoder up and messages are still only being sent as forward and in fader fx it reads up on dry/wet no matter which way i spin the jog. Does anyone have any idea what might be causing this and can offer a solution. I am willing to replace the jog or sensor if needed but not clear how easy a task this would be.
BTW the VCI updated to 1.4 first time and is in perfect condition apart from this annoying fault. Certainly worth salvaging.
Any help would be greatly appreciated.