I have Three Gen 3 Glocks , 32, 23, and 36 and one Glock Gen 4 19 and all four say on the Slide and Frame Made in Austria. I have never, with all the Glocks i have owned over the years ever experienced any rust inside or out and i carry them in a IWB Holster 95 % of the time. If for any reason you had a problem with the Glock finish a trip back to Glock would get you a new finish . My opinion, a piece of glass would rust before a Glock would .
+1 I have not owned as many as you have but I have never had an issue with rust nor has my younger brother who owns them and he lives in humid Florida.
