Epson Artisan 810 - Clearing a Paper Jam (Advanced)

I have an old Epson Artisan 810 All-In-One color printer. This morning I got an actual paper jam while duplex printing a document.
I removed the jammed paper, including the torn corner piece. I thought I had a full sheet of paper removed.

The unit keeps complaining about a jam.

I have taken the unit apart - all the removable pieces - and checked everything, with a flashlight.
Paper Tray, Document Feed Cover, Duplex Attachment (and opened it too). Manually moved the print head to look under that too. Can't see anything.
It still thinks there is a paper jam.

Looking for ideas. Just bought new ink.

Huh.
Nevermind - got it.

I guess you just need to take it apart and check everything 5 times (not 4) to clear the jam.
I did have a small black plastic cylinder about the size of a pen clicker cap fall out this last time. Oh fun! what's the worst that can happen!