I have a theory:
Mobil 1 is trying to be a low phosphourous SL oil, so the ZDDP levels are low. In order to have both a friction modifier and an AW in the oil at sufficient levels, and to compensate for the low ZDDP, moly is added.
M Delvac 1 also has high levels of Borons, which act as additional AW additive and is cheaper than moly. The borates also act as detergents and slight friction modifiers as well.
[ March 16, 2003, 10:53 PM: Message edited by: MolaKule ]