I run Mobil 1 15W50 in my 300TE and 500E gas cars; the head was just off the TE (165k mi. on the original valve guides) and the inside of the motor was spotless.
I run Mobil Delvac 1 in my 300D. I've only owned it for 3 days, so I can't back up my preference with any facts other than I know Mobil 1/Mobil Delvac 1 to be high grade oil.
"If everything seems under control, you're simply not going fast enough" --Mario Andretti
1995 E500 street car
1986 Porsche 944 Turbo S track car