Quoted from trinity9:
The only thing I'm missing at this point is the ability to push "down" while in service mode. The down button won't register. I imagine I will have to have them send me a new button assembly.
I presume the other service buttons work. In most menus, you can use "up" to wrap around.
Even so, I'd check for a loose connection somewhere. Look on the button assembly itself, then follow things up from there. It could be something as simple as a pin not fully seated in a connector shell.