So I've pulled apart the Hitachi/LG DVD drive that wasn't working (out of the v1.6 Xbox).
The gear for the drive tray & lens assembly lift has stripped teeth underneath
I had a look through boxes of spares and can't find a replacement gear, I even popped open some old spare PC IDE DVD drives to see if there was something suitable but no luck.
The tray works, but the stripped teeth are for lifting the lens so it can't even try to read discs atm.