As I recall, the cartridge stops are held in position by a "Pivot Screw" and a "Pivot Screw Nut" that mounts thru the side of the reciever. The problem is that the nuts back off and will sometims get trapped within the working parts. Others simply fall out. This is of such a magnatude that our host has had aftermarket pivot screws and nuts manufactured and sells them in a kit form..That said...about 75% of feeding and extraction problems with this design are traced to that part. It may look like the screw is in place from the outside...check the inside..it may be loose!