Those marks are 'precision' grinded, all of them perfectly even and a perfect line in between. One observation of things that occur in nature is that they never occur in precise, laser cut, straight lines. Natural wear, the path of a river, the score marks on a tree from antlers, glacier grind marks on rocks are somewhat uneven.
If you ever are looking for a lost arrow in the dead leaves on the forest floor your eye may catch an unusually even coloration of the arrow shaft since nature has variations of dark and not a perfect shade all of the same color, or you may spot it since it is exactly straight laying on a forest floor with lots of uneven lines (leaves, sticks, cracks in the soil)
You can see that the air leak actually comes from a spot on the pipe where there is a deeper unusual crevice/crack (flex or wear and tear?) Then the erosion marks are in a spot a bit distant from the crack. Those erosion marks and the straight line ridge in between look like something besides a random gnawing mark.
But then what would lie against it or rub against it?
