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The slight bend is normal. It is due to the geometry of the CRT. The greater the deflection angle, the greater the bend.
The 15GP22 color CRT has a flat panel screen mounted internally within the tube. Because of this, the pincushion is very noticeable.
Wider deflection angle tube used pincushion correction. For monochrome sets, permanent magnets were used. For color, the introduction of the 25" rectangular CRT in 1965 required dynamic pincushion correction circuitry because permanent magnets would affect color purity.
I still contend the bell of the replacement 16GP4 has become slightly magnetized and removing the tube and carefully going over it with a degaussing coil will alleviate the problem.
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