I am looking for the tuning motor for a Truetone D-727.
The gears are ok, but the motor is weak.

I'm not familiar with that model but often radios with motor-driven tuning have phase-shift starting capacitors that deteriorate and will not allow the motor to self-start. If the motor is "weak" this would be something to check. If the motor winding isn't open (in which case the motor wouldn't run at all) and the bearings aren't dry, there is no other reason for the motor to have poor starting torque.