Depends how long you want to keep the car. At 160K miles I dropped $2K for a head gasket swap w/ associated labor on my 3.0i. The thing was overheating once in a while and oil was mixing with coolant. I'm at 229K miles now and it has run solid ever since - looking back, the $2K was worth it for (at least) another 4+ years and 70K miles...