Pete,
The fact that the abberation is still there with a different camera suggests the problem is in the camera's connection to the scope OR the scope itself. If you can, make a note of the elongation and then rotate the OTA 90 degrees without disturbing the camera and see what, if anything, changes. I'm not familiar with your scope but my FLT132 has a similar problem which I'm almost certain is due to the focuser not being square to the optical path. The suggestion about CCD Inspector is good but you have to pick as even a star field as you can.
Charles
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