[drsimonwong]

No data to back anything up but my mechanic puts 15W40 mineral oil in my engine since it came under his care about 6 years ago and he's been using this weight for ever as far as I know. He's been working on 911's since the early 70's so I guess that's enough real world experience.

No leaks what so ever in my 120k car. Hardly uses a drop, except after a hard track session the dipstick mark drops a 1/3. Our summers are hot and winters mild to give you an idea of the environment.

I do remember looking back at the service history where 7 years ago one owner switched to Mobil 1 and " leaks attended to" was noted on the next service entry roughly just when new owners bought it and took it to it's current mechanic.

Simon