It's like religion... everyone has their own preference. Some people swear by dino-oils. I prefer synthetic.

All I've used for the last 10 years (in any of my cars) is Mobil 1. It's the most recomended sythetic out there. Take a look at all of the high-performance factory cars out there, and most will have Mobil 1 as a "factory fill". BMW, AMG, Chevrolet, Ford, etc use it.

I tend to change the oil every 6500 - 7000 miles (Royal Purple and Amsoil say you can go to 15K with theirs). I use a high quality filter (Wix). Avoid Fram like a bad case of herpes.

There are study after study about this. But the big things that keep coming up: higher detergent level (vs. Dino oils), better "shear resistance" (mocules being sheared during engine operation), and a synthetic base (vs. crude oil).

If your engine leaks oil after going to synthetic, it's only because they were there to begin with. All that the synthetic did was remove the crud blocking the leak closed.

My $.02

- P Roth
'92 GS