I own a Toro ZTR. Since it is for home use I do not put a lot of hours on it. With the lack of rain last summer I only have 64 hours in 1 1/2 years. The owners manual says to replace the air filter every 200 hours or yearly. My question is why every year? I believe in keeping my mower in good service but that seems like overkill in my case. an air filter should last 200 hours of use no matter of the time involved. The filter looks new.