Z1 magnetic oil drain bolt, along with my first UOA. I've been using Castrol Edge Titanium for the past 30,000 miles since I got the car at 60,000 miles. After reading the oil thread here and The370z.com, I decided to make the switch to Mobil 1 0w40. First impression is that on cold start (following morning was about 35 degrees F) it was more quiet and motor seems more 'smooth'. I am happy to have made the switch.