What indications do you see that indicates the arbor requires a 'fix'?
I found that filing or sanding is much more effective if I file or sand in two directions 90 degrees apart from each other if possible. It seems to remove material faster when using a course file or sandpaper. And the cross pattern removes the file/grit lines better when using a fine file or sandpaper. In fine filing or sanding the second direction is done with slightly less pressure to just take out the lines the first direction leaves. I don't know if that is correct, or even if this observation is anecdotal, but it seems to work.
So when I filed/sanded this barrel I followed that train of thought. It was difficult to file parallel to the bore as the stroke was somewhat 'stunted' in one direction. While filing perpendicular to the bore required a curved/circular motion that I'm not sure was following the curve of the barrel very well. Sanding on the other hand was fairly easy. I used the curved sanding blocks to sand parrellel to the bore and mixed in the shoeshine method to get the cross sanding.