Air leak help needed

[ttikalsky]

Not sure what the part is that the air is leaking from but hopefully
someone here does. Under the front left corner near the steering
gearbox is a black flat "device" with 4 air/vacum line connections.
There is a fifth nipple that is constantly evacuating air. The rear
suspension drops when I shutdown the main engine. Sometimes the front
suspension also drops and one time the air brake system pressure drain
and the suspension remain inflated. I am guessing the black unit is a
diaphram for pressure balancing but not sure. Anyone know what this
is and where I can get a replacement?

Troy, Waconia MN 83FC33