I just fixed my 04 wr450 starter motor that went bad. The starter new is around $260. It's actually not that hard to fix. The brushes were worn out and just needed replacing. If anyone has the same problem you can get new brushes for around $17.00 shipped to you. The brushes are $10 and the shipping cost me $7 to florida. The brushes can be ordered from stocker's starters @1-888-786-2537. The part number is B-16 brushes and tell them it's for a yamaha
wr450. I called many places that rebuild starters and none of them had brushes available except these guys. The manual tells you how to remove the starter. All you do is remove the header, and 3-way oil line, and then pull the two bolts for the starter. Remove the starter and unbolt the 2 bolts holding it together. Separate the starter and pull off the end caps. You'll see two brushes. One is screwed and the other sodered. You'll have to re-soder the one. It's a bit tricky getting it back together as the springs keep pushing out the brushes. You have to push them in all the way, holding them with your fingers, and put the rod in as far as you can and have it press on top of the brushes. Then you use some kind of pick and pry one brush all the way in and slip the round rod thing down past the one brush. Then use the pick to do the other brush and close the starter up and bolt it back together. Then reinstall. If this is too hard, there are usually local places that will change the brushes for you for $40-75. Hope this helps someone.