Why would there be oil in the intake manifold?

[Anton CH.]

Welp, today I decided to use some free time to clean my throttle body. To my dissapointment it was fairly clean. However, I discovered quete a bit of engine oil in the intake manifold (where the throttle body meets the manifold). It was in light brown color, similar to new engine oil color. This can't be good right?

[winfred]

normal, it's from the pcv system, the motor breaths a mist of oil from the valve cover, it's the reason for cleaning the throttle body