Thanks for the responses thus far. I will call Glock on Monday to see if I can get a new recoil spring.
Voyager, thanks for the photo; that is not the mark. The mark was not there before I shot it. The mark is near the tip of the little bullet shaped mold mark forward of the mark to which you refer and behind the serial number plate slot. It is a minor gouge like mark.
Not too concerned about the mark. I just think it was caused when I tried to pull the slide off when the recoil spring metal end may have got stuck there.