(knock on wood) Well, call me a victim of marketing, but I recently switched to Valvoline Max Life (synth blend) in my F150 and it appears to have stopped a slight rear main seal leak that I've had for some time. Prior to this, I used Motorcraft 5W-20 for nearly 75K miles. Now, I'll probably stay on MaxLife 5W-30 or possibly go with the 5W-20 since I've read that Valvoline tends to formulate this oil toward the heavier end of the viscosity. One issue that bugs me is the MaxLife bottle says to change every 3K. Is this just their general suggestion or is it a specific mention for MaxLife? 6 quarts of this stuff is about $6 more than my usual Motorcraft, so I'm not about to shorten my OCI from my normal 5K-5.5K.