Duplex printing/copying results in paper jam.

[BrockwellTech]

 Any form of duplex use - printing a 2-sided document or double-sided copying from the ADF- results in a paper-jam, I think as it rolls back into the duplexer.  Indeed, I'm not sure if it ever gets back into the duplexer itself, "scrunching-up" between the back of the printer and the duplexer.  Single-sided printing not a problem.

The printer worked well on duplex printing before I replaced the fuser.  But has not worked at all since the first jam.  I'm only able to work with single-sided documents, producing only single sided documents or copies, though no problem with multiple single sided copies.  I've stripped down the duplexer, and as far as I can tell, there are no missing rollers and the springs look pretty good.  Perhaps the cog - drive mechanism of the duplexer is defective?  This is a repost and I am also having the exact same problem.   Has anybody ever seen this problem?

[Repairatrooper]

On the upper left side there is a solenoid that activates the duplex, make sure it is working