Same thing happened to me a while back... a Ver.2 tho:
http://www.pbase.com/nervikaire/image/53025399
The reason of the break, in my case, was totally external... Slipped on a spot of ice, didn't have time to put the stock on my chest, so it was the first thing to hit the ground. The screw holding the stock cracked the gearbox. I didn't realize it at first so I got back up and started shooting again... Major failure hehe