Pincushion distortion on Sears 528.41881220

[trinescope]

I'm working on one of these 1973 Sears 19" sets and have it working pretty well except for noticeable pincushion at the top of the screen. The pincushion adjustments have some effect, but not enough. It gets really noticeable with titles or DVD player menus. The CRT is the original, not a rebuilt or replacement. Anyone have some idea of what to check for? The circuitry appears pretty minimal for pincushion correction.