Patches and discussion for Ensoniq VFX family

Does anyone know how to clean or replace one of the sliders on the 
VFX SD?  My problem is that when I play back a sequence that I am 
working on, the playback tempo changes on its own.  When I move the 
slider, I can get it back to where I want for a bit before it changes 
on its own again.

I think that the slider is maybe corroded and causing this problem.  
Came to this conclusion after finding some ?rust? that is showing on 
the headphone jack.  I bought this from Ebay a couple months ago from 
someone that apparently did not store it very well.  

If you have any other ideas about what may be causing this please let 
me know.