Hi Bryan. The problem is the movement of the clouds in the sky over the time of the shoot. It requires that I use a different healing source to get the colour and cloud texture right. Because I need to use a different source, automating the process won't work. I thought I might be able to get away with it but it turns out not.
Watch, just above the building to the right of the tower, you'll see what I mean. That's the result from using the same source to heal the dust spot.