If you get the metal version, there's a bit inside the slide that breaks off under certain circumstances. I'm on my third slide already. It doesn't seem to affect performance. It seems to be from firing a couple of full mags in "Terminator mode" - it's only ever happened to me after that.
The nice thing about buying from someone like Mike C at Elite is that he offers a one-year guarantee. He's replaced the slides without fuss each time it's happened.