Like I said, I have absolutely no idea how any part could wear into the frame? The wear location is in front of the slide lock lever. The only metal part near that location is the barrel and recoil spring. It is impossible for the barrel to touch it and if the recoil spring "somehow" scraped it you would know immediately.
Send the frame off to GI or have an Armorer check it out. Please by all means keep us posted as to the diagnosis, inquiring minds want to know?