air intake - oily residue




i noticed that the splitter was covered with an oil residue inside.. i wiped it clean, but was wondering where this is coming from...?
the throttle body had some gunk on it too, so i sprayed it down with "CRC Throttle Body and Air Intake Cleaner" and wiped it clean.
Any ideas?
By the way, what is the tiny hose connected to the driver's side intake box for?
https://mbworld.org/forums/c32-amg-c55-amg-w203/238486-25-pcv-solution-c32-diy.html



