When my kid got an '02 CRF 450 I started scouring the web for everything I could find on the older bikes, so I could go through it and fix/ upgrade anything I could afford to.
Apparently the standard type design was creating a vacuum/cavitating behind the impeller that was causing the seals to leak.
By adding a small hole to the impeller, it not only equalized the pressure behind the impeller, it actually creates a little positive pressure, which helps maintain a much better seal.
I put two holes in my kids '02 (opposite each other) and never had a problem.
In '06 Honda produced their part with the hole, and it will retrofit onto any prior year CRF450.
The part number for the new item is: 19215-MEN-850.
Tuck\o/
