Does either pot work ? I suspect the separation might be one of their fancy play pots, it moves one pot so much and then the other after like 7 degrees or so of rotation. The trace rotation can usually be subbed anywhere, it should rarely need adjustment. Most of the need for it is because of tolerances in the CRT, not the Earth's magnetic field. if it was the Earth's magnetic field you would see the trace move if you had a speaker next to it, the poles of the Earth are very weak.
Jeff Urban