Yesterday I purchased. glock 30SF, brought it home field stripped it for initial cleaning and I noticed some "brown" almost look liked rust on the slide towards the rear, it obviously wasn't rust because it came off with cleaning, just was wondering what this was? Is it stuff that they lube it with at Glock? Never noticed it with my other Glock that I had? Just was curious if this was normal, test date of this firearm on the envelope of the spent casings is 2-13-2012 Thanks for the info!