I have a 2010 Road King with 13,000 miles. There is oil in the air filter at the end of a ride. The first thing I checked was the oil level. The bike is not overfilled, but the problem continues.

 

Welcome to HDF from the UK.

Your engine breather vents into the air cleaner, to burn any oil vapour, rather than dump it out of an open tube. Call in the Touring forum here, where you will find past threads on this. You are not alone!

 

ET crankvents to create a vacuum in the crank case and vent them to the atmosphere. All engines have some blowby; the rings have gaps. How you control the blowby is up to you but venting it back into the combustion chamber is the least attractive option but meets EPA requirements.