Collimation Problem?

I have a problem with my 130 Star ED refractor. This is the f-8, air-spaced, two-element version produced during the early 90’s. I think it may be a collimation problem but before I tweak it, I want to hear some opinions. When I look at the inside and outside focus diffraction patterns, the airy disk appears to be in the center with the rings concentric. But – when I look at a bright, at-focus (in-focus) star, which shows several rings, the rings are brighter on one side than the other and the bright side shows a little red color. I’m examining the diffraction pattern at 250x. Any thoughts?

I would guess that the two elements of the lens have shifted in relationship to each other. A trip back to AP is in order.

Philip