Eureka...I found the article in Patrick Bedard's column in the November 1999 issue of Car and Driver. The article was titled, Searching for the right motor oil for "keeper cars", and he had interviewed Ed Kollin, director of R&D for Lubrication Science and ex research chemist for Exxon.

Kollin's advice was as follows:
...for an off-the-shelf blend, he would choose a "heavy duty" oil intended for diesel trucks. Instead of SJ on the can, look for combinations that begin with C (for compression ignition). CG-4 is the latest. A few blends meet both C and S requirements. While the oil part of these deisel oils has the same lubricating qualities as passenger-car oils...the diesels get bigger doses of the additives; up to 80% more ZDDP (the primary anti-wear and anti-oxidant additive), and 30 to 50% more detergent, dispersant, and corrosion inhibitors.


------------------
Dean Albrecht
94 E500
99 ML320