For me, I’m fine with exaggerating this feature to make it visible. The main idea is to give a lip for the oil wash to settle on. I went back and used a pointed q tip with horizontal strokes on the patch as opposed to vertical on the rest of the car. It helped build up grime on the lip and set it off much better. This also makes the rivets on the patch fade away- which is good because there appear to be less of them on the patches.

From what I can tell these got repaired on an as-needed basis. I model 1965 though, so any car that lived that long probably had something done to it. I’m sure one of the PRR die hards can give a better answer. 

Mike Clements