Had this exact decision last year on a Fanuc servo motor, 10 years old, intermittent encoder faults plus bearing noise. Got quotes for both options.
Repair (third-party rewind shop): $4,200, 3-week turnaround, 1-year warranty. They replace bearings and rewind the stator but reuse the housing and shaft. The encoder was extra — another $1,800 for a new Fanuc encoder.
New OEM motor: $14,500, 2-week lead time, standard warranty. Factory refurb from Fanuc was $9,200 with full warranty like pete_retro mentioned.
We went with the factory refurb. The math worked out when you factor in the risk — a rewound motor running a servo press is not the same as a rewound motor on a conveyor. The position accuracy requirements are way tighter. Our maintenance guy said he has seen rewound servo motors drift on position repeatability after about 18 months because the thermal characteristics change with the new winding insulation.
Rule of thumb we use now: if the motor is under 7 years and it is just bearings, repair. If it is encoder plus bearings plus noise, refurb or replace. The downtime cost of a second failure usually kills any savings from a cheap repair.