Well ... judging by some of the vintage machines I've worked on, those motors have lasted a very long time. I think my oldest motorized machine is from the 30's and while the external wires needed to be replaced, the motor still ran. Bear in mind these motors are external unlike the motors on our modern machines.
I have not had the guts to take any of my modern machines apart to even look at the motor. I have no idea if they are the same size, voltage ... etc. I'll tinker all day with the old gal's, but my modern machines go to the machine doctor.