This is the after photo. A plain blue-sky shot at 17mm, f22. No evidence of vignetting now. I used a Dremel tool with 100 grit sanding drum and slowly sanded away about 2-4mm from all the visible edges. The corners needed some sanding as well. This sanding was followed with some 320 grit wet/dry paper, dry. Then some 600 wet/dry paper, wet and finally 1200 wet/dry paper, wet. In the end I had a semi-polished finish. Not very shiny, but no visible scratch marks. Looks like I had a few dust bunnies on the sensor.