Occasionally an Ampico B roll drive motor must be re-wound. After
brushes, brush holders, shunt resistor, ballast resistor, open
circuits, etc. have been checked and found to be OK, re-winding may be
the only fix.
One company I have found that can re-wind these motors is Eurton
Electric (http://www.eurtonelectric.com). These folks are great to do
business with. Be sure to indicate the direction of rotation, as mine
came back running backwards.
The cost of re-winding is around $245, unless other problems are found.
That is far less than the cost of a replacement, if you can find one.
The only replacement I located cost $700.