Wipe out as much as you can without hurting the motor then use Breakclean and hose it out. Breakcleaner disolves oils and greases as it cleans and it won't hurt the wiring.
No the field coil and armature won't need to be rewired.
You'll need to really read forum member Rain's tutorial
{
http://vssmb.blogspot.com/search/label/rewiring }
before you get to going on the wiring.
I've done one potted motor and it was easy. Well compared to wiring a house it was easy.
Joe