If the seal on the pinion yoke is leaking there is very little room to be able to replace it in situ.
In order to replace the front drive-shaft, three things:-
1. Replace the centre bearing as well. The centre bearing is just a standard bearing in a pillow block. Any Bearing Supplies will supply you with that bearing. Just replace it and use the same pillow block. You do not have to go to Kawasaki for the bearing.
2. Make sure that you reposition the universal joints at either end of the drive-shafts opposing one another.
3. When replacing the drive-shafts, have a second set of hands with you to lever the centre bearing pillow block over. There are elongated holes where the pillow block mounts. It triangulates the drive-shafts to push the universal joints into the yokes at either end.