I had a generator quit generating on the road one time. I pulled off the band strap, reached in with a finger nail and pulled back on the brush springs and let them snap back onto the brush. push started the truck and it began generating again.
The brush holders just had enough road grime to prevent the springs from pushing the brushes against the commutator once the brushes got worn to the point of no contact. Sapping the brush springs dislodged the grime.
You may be able to do the same thing with the starter brushes.
