I recently purchased a 1990 MKIII with very little use. Last night after a range session, I field stripped it for cleaning. I noticed something strange on the rear locking lug. On the right side of the rear lug, there is a scrape on the top of the lug. I checked the locking lug recess in the slide and there is no burr that would cause this. At least none that I could see. I'm shooting PMP and Wolf ammo, both 115 grain. Is this scrape normal?