@MolaKule replied in the VOA thread with this:
Sulfur containing compounds in lubricant Additives:
ZDDP (an ester of Zn[(S2P(OR)2]2); Zinc, Sulfur, and phosphorus.
Spikes, H. "The History and Mechanisms of ZDDP". Tribology Letters. 17 (3): 469–489, (2004-10-01).
Calcium and Magnesium...