Let us start with some facts. The barrel and slide of the Glock are finished in TENEFER, a chemical hardening process that were the EPA to allow it into the United States would change the gun manufacturing industry forever. Why? Because it gives the outside finish a Rockwell hardness 1 point below a diamond. Glocks claim not mine. In other words, it (the barrel and slide) will never wear out, and I have only seen one with any corrosion, and that was after an officer left a Glock in the trunk of his car where he had also left a car battery which had turned over. Did it ruin the pistol? No it was still in operating condition but, UGLIER!
When I went to the Glock armorer school in about 1995 in Dallas Texas, the instructor had a Glock 17 which had fired a little over 250,000 rounds, which he invited us to shoot on breaks and lunch, AND would furnish the ammo. Requirements? Record rounds fired. It (barrel and slide) had at that point I believe, gone thru 3 lower receivers, and between 3 and 5 trigger assemblies. At that time, lower receivers were about $37.00, and other parts to me were free because I was also an instructor. Does that answer your questions?