standard w/ rebuilding the PSD is to replace the oil cooler because of possible contamination from the oil side of the cooler.
As Hheynow mentioned someone mentioned soaking thiers in CLR to clean it out however I'm not too certian about how well that works or if I would trust it especially on a complete rebuild.
Both IH and ford specifically itemize a NEW not rebuilt oil cooler on the 7.3 when ordering a crate motor and when a mfg chooses to replace entirely rather than rebuild leads me to believe that they have seen problems in the past with attempting to clean & reuse oil coolers.