How common is it for these to ware out and need replacing? Has anyone been through this? I have seen it only one time on a machine about six years old!!

Thanks Speedy, What a great answere!!

It depends on the brand, use and frequency of water box change.  On a Schwing 9" jugs, with high volume pours and daily water box changes a set of barrells will last around 500K yards w/o flip.  House slab pump more because of decreased velocity, 10" less b/c of less material.  All other manufactures use chrome lined barrells which last as long as the chrome does.  Change cups when needed and drop the water box daily for max life.