Thank you for the suggestion. Yes I have given that a try as well, but sadly that makes everything go askew. I set it with the input shorted to get a straight line across the center graticule and it appears the trace rotation is set correctly to get the tops and bottoms of the waveforms where they need to be.
I keep wondering if the shield around the picture tube is maybe somehow magentized or something like a trimmer capacitor on one of the horizontal stages (generator/amplifier) is throwing things off.
It is really something of a head-scratcher.
Thank you and best regards,