Eric,

Do you have two complete pictures side-by-side, with a bar in the middle? If so, the horizontal oscillator is running at exactly one-half frequency (7,867 cps vs. 15,734).

If you have only one complete picture with the left and right halves reversed, it is a phasing problem.

Is this a synchroguide horizontal oscillator? If so, it may need the stabilizer coil adjusted with a scope. The synchroguide system uses a single 6SN7 tube, has no AFC diodes, and separate slugs on each end of the oscillator transformer can. The slug on the bottom (under chassis) is the stabilizer adjustment. The top slug is the oscillator frequency adjustment.