Didn't get a lot of replies which is okay. I think I figured it out with help from some friends. I worked back through my workflow in Pix and concluded that I had a bad gradient in my Master Dark frame. I used my Alnitak flat panel for my flats then just turned it off and used it as the "cover" for the scope to take corresponding darks and bias. Ah! But there was light managing to get through the translucent front facing material of the flat panel. So I reshot my darks and bias with the actual scope cover on and the problem was resolved.
So in case this helps someone else ... that's what I think is the answer.
Stuart
