Hello fellow Glock owners, I have purchased a gen 2 17 upper for my gen 3 22 and upon inspection noticed there are these deep lines that appear to resemble hairline cracks at the lug of the barrel. My G22 is fairly new and there are no marks when compared, but I suspect the finish on the gen 3 may also be a bit superior. There is one specific one at a stress point that won't go away despite scratching at it. This concerns me as the serial dates the barrel to 1992, which means it may have been through a lot and I am afraid the lug will break off. I am so paranoid about this that I have taken sand paper against it and it has become less visible, but is still there. My question is, is this mark a scratch created from the locking block from normal use, a machine mark from the factory during manufacture, or a crack due to stress? Do your gen 2 glocks have similar marks? Attached are a few pics, thanks for any insight!