I give for very cheap broken Pioneer DVL-909, I repair by myself many problem, but I have still one problem:
Player work now perfectly, but he have problem play Side B, the laser unit stuck on top and didn´t move ...
I find this plastic part inside the player:

I may be wrong but it looks like a plastic bracket that sits on the bottom of the player to keep the videoboard in its place...
It reminds me of that anyway...
It holds down the board somewhere IMHO

Agreed, this holds a board in place. As said usually on the bottom. On some CLD units it is on the side to hold the top board when you swing it out for debug.