I had a similar problem with an Ampico B roll motor some time ago;
I was advised to find a restorer of antique fan motors.  There is such
a man here in the Dallas area, and he was able to fit new brushes into
the motor successfully.

Further, I'm told that it's common to need to replace the wire-wound
resistor which attempts to reduce the contact sparking in the speed
governor.  Such resistors are becoming less common these days... It
will be especially difficult to find one which will physically fit into
the cramped space provided.  Electronic supply houses which specialize
in obsolete components are likely to come to the rescue.

The resistance value in ohms?  I've forgotten, but Dave Saul gave me
the answer when I needed it.

Bill Flynt
Dallas, Texas

 [ "Ampico Service Manual 1929" says the wire-wound resistor that
 [ shunts the points is 360 ohms for 120-volt 60-Hz mains power.  Two
 [ resistors of 180 ohms (a standard value) can be connected in series.
 [ See http://www.mmdigest.com/Gallery/Tech/Ampico/spoolmotor.htm 
 [ -- Robbie