Boy, I’ve been whining a lot lately, haven’t I? Let’s look at a pretty picture for relief:
This was actually taken in the spring of 2014, but I had given it up as hopeless because I didn’t take flats (I have no excuse for my behavior. 
) The stacked lum was covered with dust donuts, both dark and bright. After much work in Pixinsight - two dynamic background extractions, with about 9000 sample points - plus an artificial flat in Photoshop and a ton of cleanup in both programs, I managed to salvage the data. I’m still shooting through Bortle 8 skies, of course, but I’ll take it. Full details are below the image.
Kevin