An underappreciated fact: extreme-pressure gear oils protect only when and where the oil film fails. Sulfur-phosphorus additives stay dormant in the bulk and react at hot asperity contacts, forming a thin sacrificial layer that resists scuffing during shock loads or slow, high-torque meshing. Early naval reduction gears pushed this chemistry forward, and the lesson remains relevant. The tribofilm is more reliable when water is kept out; dissolved moisture can hinder film formation and spur micropitting, a concern in humid, salt-laden compartments. Good demulsibility helps water settle for draining. These ideas are embodied in Reductor TIN 220 CLP.