Unfortunately, there are several things that can go wrong with the clock. The biggest problem is the failure of the plastic gears.  There are eight gears that turn the display discs and these gears are made from Nylon formed around a metal bushing. As the plasticizer in the Nylon evaporates, the gears shrink slightly. Because the gears are formed around the metal bushing, they cannot shrink without cracking.

Often the cracks are obvious, and the clock still runs.  However because the crack acts as an additional tooth, the disc slowly loses time.  In other cases the cracks have not reached the outside circumferance and the clock continues to work correctly.  The crack will continue to progress and will eventually split completely.  This often happens when the clock is put back into service as the movement of the gears causes additional stress.

The correct lamps, the 48A telephone lamps, are increasingly difficult to find. The lamps are wired in series so if one burns out, they all stop working.  There are rumors of an light emitting diode (LED) replacement.

I also have added information on how to remove the works from the clock and how to package the clock for shipping.

I also have some information on obtaining replacement gears and lamps.