So I come in and turn on the PC that I powered down while I was at GaFilk, and I discover that the fan in the external hard drive enclosure isn't spinning.
I don't actually know when it last worked. I'm not absolutely positive it ever did. I don't know if the drive runs hot enough that it actually needs the fan. But I do know I would be rather honked off if the drive bit the wax tadpole, so I think I need to power it down rather than risk leaving it running over night.