My 1987 Toro has an oil soaked sponge-type breather, and there's a tube from there to the crank case, presumably to vent it with clean air. Unfortunately, when I tip her front wheels high (which puts the breather, carb and spark plug up in the air - they're all at the front), oil runs into that tube. Then when I set her back down, the oil continues its journey into the breather and straight into the carb. The wonders of gravity! This must be why my manual says to drain the gas and oil before changing the blade. I've recently added a fuel shut-off, so that helps a little...