That is the "breather" hose connection....LEAVE IT ALONE. The PCV Valve is on the other bank of the motor UNDER the Upper Air Intake manifold. Yes it has to be removed for PCV Valve replacement. and if original that is quite probably the source of your concern. Only other reason would be from excessive internal engine compression blow by.
Just a side note...Is the filter SOAKED with oil or just a slight amount in the corner where the hose goes into the air cleaner box? IF oil change was just done, there is the possibility that too fast a pour into the valve cover can cause a backup of oil that some could run down the breather tube into the air cleaner. Otherwise just a small area is pretty normal for a car of this age. Not a lot of info was given, and there are a number of possibilities ads to actual cause.