8400 Phaser has paper jams which leave junk on the drum.

There is probably a tiny sheet of paper stuck inside the printer somewhere which is causing the jam. You basically have to find out where the previous jam was and check the rollers to see if they are clear.

If it is cuz the cleaning sheet is too stiff, then you may need to feed it from the manual feed tray.

There are no less than 5 places on this model where you might clear a paper jam. Is it possible you still have a small bit of paper stuck somewhere?

http://www.office.xerox.com/userdoc/P8400/8400_Web/videos/paper_jams.html

Normally indicates that the mintenance kit is drying out and not properly lubricating the drum.
Or non xerox ink sticks have been known to cause that.

Pull the maintence kit and look in the hole. If your printhead maintenance pivot plate (that the maintenance kit hangs on) is white, it needs to be repalced. It's probably cracked and flexing, not lubricating the drum properly. At the same time, the DM camshaft should probably be replaced. The cams crack on the thin side and rotate on the shaft, causing the maintenance process to malfunction.

You manually rotated the aluminum drum? Since you did that, I would suspect you have the print head wiper blade stuck between the drum and print head. The code you are getting it caused by the print head not being able to move freely.
The jamming is probably due to a bad registration clutch. Common failure on that machine.
You can go to Xerox.com, there is under documentation and drivers a parts list for that machine. You can reference the wiper blade and get the clutch part number there.
Let me know what other information you may need. I will be glad to help you get it running again.

I posted a problem with the phaser 860 paper jam. I found 2 broken sensor flags and am ordering the parts.

Here is the Xerox support page for your printer. It even has a movie on removing paper jams.
http://www.office.xerox.com/perl-bin/product.pl?page=sprt&product=8400&country=United%20States&language=en#_manuals_and_documentation_

The preheat entry assembly has paper detectio arms/sensors that will get brittle and break off, leading the machine to think there is a paper jam. This problem usually will require a trained technician to diagnose & repair.

Sounds like printhead needs replacement.
Moving these printers without cool down is known to destroy printheads and of course wax goes everywhere and then everything else fails.Think about replacement

The 8400 has a known issue with the plastic that was used for the tilt mechanism on the oiling roller. If you look inside where the cartridge is removed you should see a crack that opens when pressure is applied. The high heat causes this unit to crack. You need that part. Or some good super glue. I have fixed 3 of my 8400's with this same issue.

Good Luck