Nice trick, I've used contact cleaner before on one of my Lecroy 9300's, that uses similar Bourns rotary encoders.
In my case there was enough play in the axis to let the spray flow down it.
A couple of side notes:
Protect your eyes when spraying into small holes, I once sprayed into a small DC motor at the brush holes with contact cleaner, quie a proportion flew back at me and cleaned my eye. That was painful and stressful for several hours
On cheaper rotary encoders and potentiometers as found in much (Wun Hung) Lo-Fi audio equipment where the grease just turns to stiff goo, white-spirit before contact cleaner works wonders to ease the rotation.