I Jacked up the 05 Pr. thinking that it being level, I could drain and refill with the exact amount. When I started removing the fill plug, I could hear a sucking noise indicating that there was a vacuum. I expected the level to be even with plug. As soon as normal pressure was restored, fluid started gushing out and I had to jack the front end up more to keep from getting fluid all over me. I carefully measured the amount drained which was a little over 4qts., releveled the car and put 4qts back in. I didn't notice any unusual smell but the old fluid was somewhat darker than the new, and the magnetic plug had a small amount of black goo on it. To refill, I used a small funnel with a long piece of clear plastic hose which worked like a charm. This fluid change was at 30k and I will probably do it again at 60k. I was wondering if the vent is designed to relieve pressure and operate under a slight vacuum (like a check valve) or is it possible that the vent is plugged?