Hiya
Oil can get into the inlet in 2 ways. 1 is via the breather pipe which comes from the cam cover and connects to the inlet pipe. 2nd is via a breather hole in the head which links into the inlet where both meet. Oil in the inlet is very common. Your oil is being burnt but at small amounts which you probably wont see while driving. You can block off the no 2 and just have a catch can for the no 1.
Valve stem seals is another way oil will get burnt if they are worn but again small amounts. What is the mileage of the car? service history? etc
P.S. if you drive fast more oil gets sucked in.......Hope that helps