On my recently purchased 2007 Impreza 2.5i, I noticed I'm going through a lot of oil. I'm going through a quart every 1100-1200 miles. The car runs flawlessly and doesn't smoke or leave any drips that I've noticed. The oil and antifreeze are always clean. The oil pressure switch was just replaced for pissing oil. The car has 68,000 miles and quarts of oil are going to get expensive when my work week requires 816 miles of driving to and from work. Any suggestions on where to start?