I do a lot of transparency scanning on a dedicated flatbed. About every couple months I will pick up dust debris that leaves a color streak across the images. In each case it was a result of a particle I suspect on the scanner element as near as I can tell. I would merely blow very lightly with compressed air into the scanning bay area and it has resolved the problem every time. This is the same scanner I've had for several years now, so thankfully it is resolved each time by this method. Of course the next scanned image after the cleaning is previewed at 100% + to make sure the area lost the streaking. Good luck.