He's refering to the scratches that the recoil spring makes on the front inside of the frame where the metal serial # plate is.
It's nothing to be concerned about, just turn the part of the recoil spring that is bowing out up toward the barrel. The recoil spring is trying to take the path of least resistance, so it bows out in some areas. When the slide recoils it compresses and straightens out. It will not wear through the frame and a small part of the serial # plate shows through on the inside of the frame on HK pistols.
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