The vac source most likely is located in a difficult place to see and service. It is at the rear of the engine between the intake manifold and the firewall a little to the passenger side. Follow the line from the four-way connector on the driver side, across the upper side of the firewall and you will see it.

The right angle soft connector is your likely culprit. It lives in a hot, oily environment and is usually the first to go. I used a piece of plastic tubing as a temporary fix until I was able to find the correct rubber connector. If you have big hands you may need help from someone smaller.

Let us know how you make out.