Okay so what I've done now:
sudo apt-get update/upgrade on Core and MD
rebooted Core and MD
MD still displays the Failed to Setup X
ssh to the MD and "apt-cache policy nvidia-glx-173 | grep Installed" gives the same: 173.14.22-0ubuntu11.1
"apt-cache policy pluto-boot-scripts" on MD:
Installed: 188.8.131.52.12022425542 (do note that it's different from the MD if that makes any difference)
So I reran the update/upgrade. The core now has the latest pluto-boot-scripts. However the MD doesn't want to update, even after a Core/MD reboot.
I am running "sudo" and it still says:
The following packages have been kept back:
linux-headers-generic linux-image-generic pluto-boot-scripts
0 upgraded, 0 newly installed, 0 to remove and 3 not upgraded.
I don't know how to fix that.