I have now verified that the RA drive does work properly: last night, for the first time, I took images with the RA drive running at the sidereal rate, and they indeed show little trailing. Rah!
Last night was the coldest night of the season so far: the temperatures dropped below freezing as soon as the Sun disappeared below the horizon. I discovered that the water/antifreeze mixture I use to cool the cameras had frozen. Actually, only the portion of the liquid in the small section of tubing which is exposed to outside air (between the garbage can and the shed) was actually frozen. I managed to thaw out that section by pouring warm water over the tubing. When I finished using the camera, I connected the two ends of the exposed tubing together, and kept the pump running. This morning, I verified that the fluid was still running freely. I guess I ought to add some more antifreeze...