Here's a follow-up on the mysterious "single sided" CDC (77744401) drive. On a quick inspection (rule: always
look at what you have to do before picking up the screwdriver!) I noted a pin-and-weight affair connected to the head carriage. On closer inspection, it turned out to be covered with solidified grease that glued the weight firmly to the base and a pin (which slides through the weight) firmly glued immobile in the weight. As a result, one end had become detached from its post on the head carriage:
The grease was worse than cold tar and had actually reacted with the metal of the weight and frame to make a black goo and did not yield to mineral spirits, alcohol or perc. MEK did the trick and the whole affair left soaking overnight eventually freed the pin from the weight. I cleaned everything up and applied some white lithium grease, which appears to work just fine. The ends of the pin were secured with a drop each of lacquer.
The drive appears to be 100% and reads my disks, but I haven't done an alignment check yet. If it's close, I'll just leave it alone.