I watched that video but the piece he pulled out is different from the one I have. I did manage to get it in well enough to stop the head from moving. I don't know if it was the exact same or correct place, but it seems to have worked. I called Epson the morning of the move and their answer was that most people take it out and throw it away, so they have no instructions anywhere on where/how to put it back other than the very poor diagram in the manual. No help.
Here's a photo of the piece installed, my way. There's a long flat piece, about 6-7" long, that is attached to the bottom half of what is shown in this photo. It's flat against the back panel and runs back behind the head. By unfolding the top half of what's shown, where the string is attached, it will fit snugly up at the top. As I said, I'm not sure if that's the official way, but it worked. 9900 is back in business!