What is the size of the micron for the pre filter? it might not be small enough to stop the silt that is getting in the seal pack area and killing the o rings.
Until that part is fixed so that the silt is not getting into the Culligan head... you will be replacing the seal pack every x number of months or years.
Also on the pre filter , how big is the filter that is in the housing? 4x10 2x10 or 4x20 or 2x20?