Do ESOF vacuum solenoids commonly leak?

After reading a few troubleshooting threads here I took a shot at a quick diagnosing a common HVAC vacuum issue without any specialized equipment.. No dash vent AC. Only defrost vents working.

With the key on the vacuum pump ran continously. I pulled the vacuum outlet line to the resevoir(??) and blocked the pump outlet with my finger. The pump cycled off immediately. I then pulled off the "outlet" hose from the reservoir fitting and blocked same with my finger. The pump again cycled off after what it appears to be enough lag time to reach the desired vacuum pressure. It appears that this portion of the system is working correctly.

I then went to each front hub and disconnected each hose (seperatly) and blocked same with my finger. The pump ran continously on both hubs for considerable time and I could not feel any suction on either side.

I reconnected the wheel hub lines and then disconnected the solenoid vacuum lines (black and red vacuum lines) located on the fender behind the battery. I blocked the red line coming in from the reservoir and again, the pump cycled off after I assume the correct pressure was reached.

So to have AC temporarily, I blocked the red line (at the solenoid connector)and the AC vents now operate normally. If by the rare chance I need 4WD, I will operate the hubs manually.

Also, before I began troubleshooting under the hood, I did notice that when I activated the ESOF switch on the dash, the AC vent dampers would open sending cold air through the dash until I switched back to 2WD and then it would default back to the defrost vents. This is what led me to believe that the solenoid valve might be part of the problem.

What is the likelyhood that my leak is the solenoid unit itself? Thanks.