(ET) Field trouble?

[Steve Gaarder <gaarder ecovillage ithaca ny us>]

My E15 is having problems. When I try to run the motor (in neutral) it 
shudders in the lowest speed and spins very fast in the higher speeds, 
drawing lots of current. Sounds like no power to the field, right?  I 
disconnected the armature (at the resistors) for sanity, measured the 
voltage at the field terminals, and see full battery voltage.  The 
in-circuit resistance of the field terminals is 31 ohms.  Do I have an 
open or partially open field coil?  Anything else it could be?  Where's 
the best place to get a replacement motor, or is it worth having it 
rewound?

thanks,

Steve Gaarder