The motor for the rollers right as the paper is going to go under the fuser does not come on. It works fine in component test mode. It does come on while copying maybe once in 50 tries, but it is very rare for it to work. I have loosened wire ties at the Duplex PCB and in the harness of the duplexer as well. Knowledgebase seems to point to Duplex PCB and Fuse PCB.
Double check the right motor is coming on. I had found a problem with the manual showing the wrong number in part check. And the problem was the motor. There is another motor in that tray that you can use to troubleshoot.