Hello,
I just registered to provide better repair procedure than one found on this site:
http://chipmusic.org/forums/topic/12200 … is-repair/
(I could not bump old topic since I am newly registered)
Instead of modifying/drilling your original device, I have found a better option...
I have used dental floss and sewing thread dipped in alcohol (I used pure isopropylene, but anything should work I think). You put it inside potentiometer and wipe the contacts without disassembling it. Just like you would floss your teeth.
You will make no harm to your original device this way.
This has resolved problems with my contrast wheel which caused flickering exactly at the spot where best contrast should be.