Go to your Yamaha dealer and ask for new brushes for a Warrior starter. Tear it all apart, and make careful note of what goes where, especially the tiny spacers. You can swap the one brush directly out, but the other needs to be heated and taken off, and the new one soldered on. Then get somebody (either a machine shop, or do it yourself if you have a metal lathe) to shave a little bit off the commutator so it's shiny again. Clean the groves out real well or you will end up with a dead spot. Be carefull putting it back together and it should work like new! Took me 30 minutes to do it start to finish.
EDIT: Your starter solenoid clicks nice and strong, but the starter doesn't spin right?
