I bought a second hand src mp5 skirmished it twice with no problems I then bought a hi cap mag, which unfortunately didn't fit I was told it was due to the battery wiring being routed wrong, I found someone online who changed the wire round so it was out the way, I then fired the gun a little while later just to make sure everything was ok it fired 15-20 bb's then I heard grinding I found a gear in the box to be shredded, my question is does it have to be an src gearbox or will any v2 gearbox fit many thanks robbie