Toyota Kluger 2008: Unpleasant odour when accelerating?

Shortly after buying our new 2008 Toyota Kluger Grande we noticed an unpleasant odour when driving up a hill and accelerating. We notified Toyota and discovered that it was actually exhaust fumes that were entering the car through the back window. Initially Toyota replaced the rear door with a new one, but when that didn't fix it they replaced the rear window seal with a thicker rubber. That still did not fix the problem and now nearly two years on I would like some answers, but they appear unable to provide them. As you could imagine I am quite annoyed that I am still driving my family around in a $60,000-plus car that still fills up with exhaust fumes. Have you heard of this problem before? If so, please let me know how to get this rectified and where I stand legally?