I'm an O scale guy, but one of the members of my club had me look at his American Models SD-60 locos. These are true scale locos, NS short hoods.
AAAAAnd they click like mad when going around the club layout. We popped off the shell to look at the drive line. Yep, it has a nylon type motor shaft coupler in the middle, and two black plastic output shaft couplers on either end of the driveshaft (U joints?). Each coupler has a groove that engages a T fitting on the driveshaft... at they have split inside, but only on one side of each coupler. The other end looks like an interference fit onto the output shafts.
These locos have to be 10 years old... can you still get parts? Where? Maybe someone has figured our plastic isn't the way to go? 
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