It could be a burnt motor, armature of field, or just the brushes. Since the brushes are so inexpensive, I would replace those first and see if that helps. Here is a breakdown of your tool and you can see what parts you need.
http://www.toolsandmachinery.com/index.php?cPath=2213_2300_2301_2315
Don- www.toolsandmachinery.com
April 2009