D&H C420 #508 with rear partial repaint (1983)

In the mid-1980s, just about all of the D&H's engines were filthy. They were worked hard and put away wet. This shot from February 13, 1983 shows an Alco C420 with what might be described as "extreme weathering". But note the rear hood... I don't think that is a patch of sunlight streaming onto it. Was it recently repaired and then repainted? It was common to see this type of thing on the sides when the units were renumbered, but not isolated to the rear fan areas. Hmmm...