Try an oil/air separator or a catch can (basically same thing)
Im pretty sure it would be the oil coming from your cam cover going into your inlet manifold via the PCV valve breather thing up the top
Not the best photo but look at the catch can on the left and follow the black hose around and it goes to the cam cover.. This would prevent any oil getting into your inlet. To make it legal all you have to do is run the return pipe to the inlet and wallah