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OK,
Polar alignment can be ruled out by doing a short exposure of a bright open cluster or the like. You are not going to get field rotation in a short time. It doesn't look like field rotation anyway.
I have had no experience with coma, but I don't think this looks like coma which radiates from the center outwards. your image doesn't look like this.
Flexure of the optical train is quite possible, resulting in defocused stars. point your scope to different parts of the sky to see of the elongation changes depending on where the scope points and which way the camera wants to sag.
My bet would be miscollimation. try tweeking your collimation while in focus and then viewing what happens to the stars - trial and error until you know what affects what.
2 other things, how is your guide graph? can you rule out Differential flexure and camera tilt (not orthogonal to the optical axis)? Although, as far as guiding goes, the star elongation isn't exactly all in the same direction.
Josh
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