The G36 problem i was referring to was the cracking around the hop-up, i'm now wondering how common this cracking is.
Never happened to me, and I've done just about everything to mine, good and bad. I kinda think that, what with how the gun's put together, you'd either have to do something to it on purpose, have a REALLY rough spill with it, or just plain wear it out to the point that you'd be replacing it anyway. That section is well protected, so it's not likely to break under normal circumstances. This is the TM I'm talking about, from my own experience.