Reply to erratic fader response?

This is a VCI-100 SE with the arcade mod. The left channel fader is sketchy -- its movement is fine but it's sending out choppy MIDI so that Traktor responds unpredictably -- if I move the fader from the closed position to all the way open in one movement, Traktor responds with a choppy jump up and down and back up again, sometimes shivering somewhere in the middle for a while and never making it to the top. Is there some kind of easy fix for this or do I need to get it looked at?