Humidity can wreak havoc on lots of things depending on where the seller(s) kept it. 50-60 years in a box, the grease or lubrication oil will have gummed up, and like what happened here, the carbon blocks bonded to the motor as well from being damp so much. It's kind of like a barn find car - it may be barely used and low miles, but being stored that long without touching it will ruin it.
I have a jukebox in my basement from the 1970's and it broke down in the early 2000's and haven't found anyone to professionally overhaul it on-site since then. After 20 years of disuse, the grease is really sticky and tacky and all the mechanical parts are off-sync and it squeaks like crazy.