I recently cleaned the VF and RF patch of my IIIC. Gaining access was pretty easy:
Remove the screw to the right of the meter, and the two under the left rewind knob (pull the knob up to access them). The top plate will pull up, then rotate it 90 degrees to the body, so it sits on top of the camera. This gives you access to the VF and RF optics without having to remove the rewind knob/shaft.
Careful cleaning with optical grade swabs left my camera's VF much cleaner, and the RF patch brighter.