Hm, I tested the same with VueScans infrared cleaning, strongest setting, and the results are extremely different:
If I try to ignore the compression artefacts (I should have saved as tiff) the problematic area is still visible, I would say better than 1 to 4, but worse than 5.
The line was hardly removed at all. At that point, I am so happy about having the opportunity of using FLOSS software 
!