I just sold my gun today, and it worked fine. I even got it to chrono it in Gearbox and it worked fine.
But later on the day i got the call from the guy and said after about 12 shots, the motor winds but does not shoot anymore. He called me and asked if it has happen before. I said to him and knowing about it, to my knowledge I didn't have problems, i let my friend used it when he didn't have a gun and never had a problem with it.
Is it a major problem? Because i called my friend who worked on my M4 and said that the screw that aligns the motor and the gears are off.