This just happened on our 2004 Prius at 172,500. Dealership stated this is a problem for Prius' with > 120,000. Dealership replaced a PVC(?sp) valve and said to bring it back in a 1000mi. After the dealership worked on the car, it is getting significantly better gas mileage. The bad news is that one possibility is to replace the engine at around $5600-6000.My 2005 Prius with 180K miles is using a quart of oil every 2K miles. Has anyone had experience with this?