Personally ... I would take it on instead of letting a repair shop replace the motor ... especially if your repair shop is not a highly recommended vintage shop. I saw pic's of one where the repairman replaced a featherweight motor with a larger motor and had to use a hack saw to chop bits off the featherweight to fit the motor to it.
The smoking motor COULD be an easy fix ... cleaning. It could be more.
Follow this thread
http://www.quiltingboard.com/vintage...r-t220993.html
More information on this blog
http://vssmb.blogspot.com/search/label/221 - use the links at the right for more information on motors.
I would at least try it myself, the worst you can do is have to replace the motor anyway which is what the repair man said.