How many hours do you have on it? The rings went south at the 15 hour mark. A loose piston can lead to catastrophic damage in the thousands. Well, if you catch it early in destroying the crank, you can get away with a 500 dollar rebuild, or less. Routine maintenance required!
Clean your air box until it's dry and unplug the sort of Y rubber hose connected to the air box and cylinder head. Blow some air in to clean it. If it still throws some oil in the airbox, time for new piston/rings (at least). This happened to me last summer. I crashed and the bike flipped badly while still running. I realized there was oil in the airbox when I cleaned the filter. I did what I proposed to you and it stayed perfectly clean afterwards. Is this something that started happening a long time ago? Or did you just realize that? How much time has elapsed since the top end has been done?