I was told by the dealer the oil tank is sealed, except for a one-way air valve. Their explanation is when the air in the oil tank expands due to heat or altitude change it pushes oil out. My old Homelite 150 never did this, and it seems pretty lame. Laying it on its side with oil cap open, or keeping the tank completel full might work, but none are convenient. Is the answer from the dealer true?