This happened a few years ago. G22 bought new in 2000. I brought it to a gun smith and he said it was fine. The gun shoots fine. But I've never heard of a Glock doing this. And it does not look fine, at least it annoys me. I keep it clean and lubed up. It probably has 800 rounds through it, mostly 180 Winchester fmj target. It has rubbed on something but not sure how or why. Have any of you ever seen this before?