2000 Dodge ram Van b1500 mkiii se need help identifying this part?

I can't find this part in the service repair manual anywhere. it is leaking, I looked up the part number that is on the part itself and it it comes up on ebay as a "vacuum actuator".I still can't find the part in the manual nor can I locate the gasket. Can anyone help me identify this part and what do I tell the folks at the auto parts store that I want to order?

Thank you!