Hey!
I'm not sure , but I think the Mod and Pitch wheels are in fact classic variable resistor ,like the ones for volume control.That means is a carbon surface and a kind of brush for changing the resistence value when we move the wheels.Sometime that carbon surface can get dirty or even broked.So, I should try a little contact spray for electronics on it.I have a little problem with the pitch...sometime is jumping to fast from a value to another, I should open the keyboard and take a look someday...
Vio