I would keep that sprocket around for a spare in case something happens and you needs a replacement late saturday or on a sunday or something. I too say you hit something even if it was dirt , doesnt take much dirt to hit to grind a chain down.
Stihl stopped putting grease holes in bars years ago. Then they starting decreasing stock oiler output.....
I grew up drinking Vernors Ginger Ale. https://en.wikipedia.org/wiki/Vernors oldest surviving ginger ale brand in the United States