The idea behind the preventative WP replacement is that if it fails, which is more likely the older the pump is, the plastic impeller will break, and the shards can lodge in the radiators reducing their cooling efficiency. That ends up being a bigger problem than $200 for a new pierburg WP every few years. I had mine replaced once under warranty and changed it myself at 90k when I flushed the coolant and installed a third radiator.