Hi all, As I was cleaning my gun (Glock 19, Gen 4) yesterday, I noticed some black on the piece (don't know the name) right infront of the locking block. It is only on one side. I have included pics. It's fairly new, and although I have cleaned the gun before, I may have not noticed it until now. Any help would be appreciated. *If it is normal, please keep the flaming low as this is my first gun. Thanks!! The last photo is of the same part but on the other side. Thanks everyone.