Salute Dave!
Wow. It is obvious Dave has more than the FCOM at his disposal. e.g. How many foot-pounds torque do we need to tighten those bolts?
As some suspected, the manual cable drum does not have its own connection to the jackscrew. So a failed gearbox could be a player. The manual drum could just be spinning and not turning the big screw. Or it could be jammed.
Gums...