get a fibreglass pen, and clean the sides of the brushes as well. this will improve conductivity from the hood to the brush as well. and remove any debris that may be making the brush stick. you can use this to clean the face of the brush too, and the comm as well, if its not scored deeply, and you don't have a lathe.
3M makes it, called a rust remover pen, it looks something like this:
http://www.sjdiscounttools.com/abras...nding-pen.html
its one of those tools to have in every pit box if you run electric.