I replace all Bearing Spider shaft and bearing seal. I think you should always replace the spider assembly along with the bearings and Seal. The water seal depends on this shaft to be perfect with no Pits on the shaft. Also recommend using a impact wrench to remove the 6 fine thread metric bolts. The impact hammer action breaks these loose with no damage. They are very hard to remove. Also I found that installing the Main motor bolt all the way into the spider shaft assembly and then using a large hammer will remove the shaft from the bearings better than using wood to prevent damage to the shaft. The hammer energy is transferred much better with no damage to any parts.
The Video is a great help.