After running Update Manager, a debconf window (titled “Configuring grub-pc”), popped up, requiring me to select the appropriate

GRUB install devices

for my system. I've made no changes to grub or the filesystem recently, and I don't remember what options I selected last time I did make a change.

In your case, the correct selection is /dev/sda, the first one. It's the first and only hard disk in your system, whereas /dev/sda1 is a partition on that hard disk. You can install grub on a partition, but it's a “BAD idea”.

If you had multiple hard drives and paritions, first find out where your root partition is:

df | grep /$

You can then install grub on that hard drive. Notice, this command will show /dev/sda1, meaning you have to select the hard drive on which it is, /dev/sda, to install grub into the master boot record (every hdd has only one mbr, no matter the partitions).