Well, I'm getting Glock to send me a replacement and I also ordered one from Lone Wolf. I'm not sure, but I believe the Lone Wolf is machined. I got it with the intent of using it as a non Glock model to compare to. Hopefully it will cause Glock to look at the extractor as a possible cause for these issues. The fact that they are on the 4th iteration of recoil spring assemblies without solving the problem suggests, to me anyways, that perhaps the recoil spring isn't the problem. It's just the easiest thing for Joe Sixpack to look at and say, "hey this is different it must be the problem." The fact that the newer production (since the MIM "upgrade") gen 3 guns are having similar issues should be an indication that the spring is not the culprit or not the only culprit. Granted I see a lot less reports about them having the problem so it probably isn't as frequent as the Gen 4 guns, but it is a problem none the less. The older gen's do not have the double captured recoil springs....so.... maybe it's time to eliminate the recoil spring as the culprit, or at the very least consider it an accomplice and look into the extractors as well.
I've heard that the extractor should just fall out when there's nothing left holding it in and mine certainly doesn't do that. After removing the entire extractor spring assembly and the firing pin safety parts, I have to pry the extractor out with a punch. From talking to Glock too, prying the extractor out with a small punch while everything is assembled, the edge of the extractor that goes over the case lip should come out far enough to be flush with the ridge running down the right side of the bolt face, and mine is not. The lower half of the extractor moves far enough towards the outside to clear the bolt face, but the top 1/4 or so of the extractor cannot be made to come flush with the side of the bolt face, which may explain all the excess wear on the peg of the extractor. Not the most scientific method I know, but I'm not a scientist.
I also talked to them about the slide releasing when a mag is inserted. They said that can happen when the muzzle is pointing up, but I couldn't quite understand the reasoning behind it as it was explained to me. Regardless, I then tried it with the muzzle pointing straight down, halfway down, forward, halfway up and straight up after I was told that and it does it those ways too. In the video I posted the muzzle was flat and I was holding the gun sideways and it did it then, so I don't know. Maybe the slide release has a weak spring or something.
I'm still not sure why it's tearing up the brass though. If it was tearing up the rear or cases I'd point my finger at the extractor but it's tearing up the front of the cases, that would make me think the chamber, but the scratches aren't running the case length so that makes no sense either. The only thing I can think it after being pulled from the chamber by the extractor and hitting the ejector maybe the extractor is holding on to the cases longer than it should and they're being run across the ejection port of the slide after the ejector has spun them sideways. If that's the case then we're back to the extractor, or an over length ejector, which I doubt.