Here's a bit of a stumper- I am looking at replacing third gear in a WR426 transmission, both sides (pinion and gear). I have the part numbers from both bikes. Can someone tell me, just by looking, if they are the same parts, or maybe what the difference is? I had heard that the trans for the 2004 was an upgrade from the 2003, and am hoping that I can upgrade the 2000 WR426 to 2004 WR450 specs because I don't like splitting cases to repair gears. Again and again. Headgaskets get expensive after a while. 3rd Pinion WR426- 5BF-17131-20-00 WR450- 5TJ-17131-00-00 3rd Gear WR426- 5BF-17231-00-00 WR450- 5TJ-17231-00-00 Thanks for your help, it is appreciated.