Interesting. Yes, there should be a plunger and spring, with a diaphragm. I would think you'd want to have it stuck closed rather than open (removed), since it would be recirculating pressure out of the intake manifold and back into the turbo inlet. Some have reported that this drastically reduces the amount of boost that can build, since it's normally matched by an equal-ish amount of exhaust gas from the EGR.

Does it seem like the oil was coming from there (via the valve cover vent)?

-Rog