Í really don't think it's oil from the AC system because of the color but that is a possibility since the system leaks its charge rather quickly. It's definitely got a thin film of black (most likely engine) oil on and inside it. Oil is accumulating there for some reason. If it's not supposed to be that way then my best guess is that a vacuum motor, regulator or checkvalve in the HVAC system has a torn diaphragm and blowby is getting in somehow. Hopefully I wont be tearing it off with a crowbar but it's nice to know it's only there for knee protection. (because I'd much rather jamb my knees into something steel than soft)