Vintage Synth Repair

I have a D-5 with a trashed pitchbend potentiometer - it literally  
fell apart when I removed it.   The modulation sensor still works  
fine, so I don't want to go to the extreme of replacing the entire  
assembly (assuming it's even still available) unless absolutely  
necessary.

It's a 16mm 100K pot and I assume it's linear given the application  
(?).  What's throwing me is, it has four terminals - the three normal  
ones, plus one on the other side which I assume is a ground.

I've looked at Jaycar and Dick Smith but they don't have any 4- 
terminal pots like this, and I'm concerned what they have would have  
too stiff an action for a pitchbender anyway.

Any suggestions?

Many thanks,
Lindsay