Stop back from time to time. I'll keep adding material.
However, one important reference-point link will be anchored here, up front. The information supplied will attempt to make the distinction between the challenges inherent in the 78 RPM Library Mechanism (and the M100A jukebox mechanism) - versus those of the E A R L Y 45 RPM successors, whether the 45 RPM Library Unit or the M100B and few subsequent models.
I now understand why Seeburg restoration web sites often limit their services beginning with Jukeboxes manufactured in 1951.