I'm guessing if you removed the cover shown in the photo you will find a set of gears not unlike what you find in a RC servo. The actual motor will be under the gear set. Remove the gears and clean well then relube with light grease. I've seen some of this grease turn into "glue" that is almost impossible to remove
When it is all apart plug in the motor to see it it runs. A drop or two of oil may be in order. If it is the type of motor I think it is they do not normally "go bad". They have very little torque so everything must be in top notch condition to work properly.
Good luck and keep us posted.