Got a 9 year old Craftsman 42" cut mower with a Briggs 18.5 Intek OHV engine. Just started smoking when the mower deck is engaged. Runs fine otherwise with no smoking. When the mower deck is engaged and engine is at full throttle, it leaks oil from the breather in the fuel pump and smokes from the muffler. When you open the air breather, smoke comes out of there, and out of the oil fill unit when you take the cap off. However, none of this happens when the deck is not running. So the extra torque needed to run the deck is causing some type of issue in the engine. We've had the carb cleaned and it still does this. The air breather is brand new and spotless. I'm not an engine guy, so I have no idea what might be causing this. Any idea what the problem might be? I was told that it might be a bad ring on the piston? Engine shot?