Unless the newer clocks are different... there is a thin metal arm that rotates with the spring as it unwinds, when this makes contact in the resting position (to +12v or ground, I cannot recall which way the thing is wired), then it completes the circuit and the coil is re-energized, which rotates the shaft and re-winds the spring. This process repeats about every 8 minutes or so.
I found that the two mating surfaces of the arm and the voltage (or ground) source were slightly corroded. I polished/ resurfaced both of them with a file designed to clean the contacts of a relay and it solved my problem. I may also have had to resolder the low temp "fuse".
You can determine if the clock is functional by winding it by hand and making sure it works, for a few minutes anyway. You may have to flip back a retaining latch along one of the gears or shafts in order to wind it without voltage applied.
I'll take look and see if I kept any documentation for this repair on my 74, and I consult the Bentley's manual as well.
A fine alternative is to either send it out for repair or to "upgrade" it to a quartz movement.
I prefer to make a German mechanical device function as intended rather than to replace it with Japanese circuitry.
FWIW, the clock in my 84 has stopped working on several occasions over the past month, so it too will find a place of honor on the workbench some Sunday afternoon.
BTW, I used a very high grade tool oil that was intended for precision mating surfaces on industrial equipment. 3-in-1 oil is too thin and WD-40 will become sticky (attracting dust, etc.) once the solvents evaporate.
I've heard of people using a product called "PB Blaster" as an alternative to wd40 in these types of situations but I have no idea where to get it.