Just send it to DLX, http://luxepaintball.com/support/index.html
Either sign in or make an account, then make a RMA number, click "Open new RMA". Then go from there. After you are all done give wherever you send it, GoG or DLX a call and they will get your gun up and running. Here is the DLX/GoG info thread, http://www.pbnation.com/showthread.php?t=3290354
There is no point in emailing them, they will just tell you to call them/
Also if that guy actually sent you a broken gun and he didn't tell you anything was wrong with the gun, I would file a paypal claim (if you paid through paypal) and if you didn't talk to him about it and see if you can get him to help out with the cost or something.