Today I took my throttle body off to give it an inspection and a clean, and I saw the following stain on the top of the air inlet into the supercharger... looks like something is leaking into the air inlet from the top of the the unit just post the throttle body

I know that the oil seperator / PCV has a return line which feeds back into the intake somewhere but I thought that was into the air intake (stage 2 part) ahead of the throttle body, not behind it

Does anyone know exactly what this is?? And if it is the return line on the OS / PCV, what does the little hose that plugs into the air intake (stage 2 part) do?