If the pump runs continuously without touching the ESOF switch, it is NOT the seals at the hubs or hoses to the hubs. They will only have vacuum when the switch is turned to engage or disengage 4x4. The most common causes for vacuum leaks without touching the ESOF is either the hose under the dash gets kicked and disconnected, or the PVH solenoid leaks to atmosphere. Check and make sure the line is connected under the passenger dash to firewall, and a quick check at the PVH solenoid, disconnect the vac hoses and plug them. If it pulls vacuum and maintains it, it is most likely a bad solenoid. To verify, you can turn the vacuum lines to only connect the vacuum inlet to the solenoid. If the vacuum is lost and no vacuum is present at the port to the hubs, the solenoid is leaking.
Just a quick lesson on ESOF operation(from memory a bit, numbers may be off a bit): To engage, a 15" vacuum is sent to the hubs for approximately 45 seconds, then vented to atmosphere. To release the hubs, a 6" vacuum is sent to the hubs for approx. 30 seconds, then released to atmosphere. While the release vacuum is applied, it will not unlock the hubs until that vacuum is vented.