Your servo appears to not have one.
Mine had one - it's one of the things that stop the servo from rotating past the 180 point. I removed it before starting this thread, hoping that the stop was the cause of my problem.
It appears the pot in your servo is either detached from the servo horn, or the pot has been damaged in some way.
I have attached pictures of one horn to show that the pot rotates with it, the movement is smooth and clean. I have also measured the resistance of the pot, and it seems fine (approx. 3.35kohm).
If I take off the metal "V", there will be no stop for the pot, and it should be able to rotate freely. How will this help the pot from locating different positions throughout its rotation?