A lubricating composition for use in heavy duty diesel engines which is formulated to allow the use of organo-molybdenum compounds but which overcomes the issue of Cu and/or Pb corrosion and also maintains elastomer seal compatibility. The lubricant is characterized by having a composition comprising (A) an organo-molybdenum compound, (B) an alkylated diphenylamine derivative of triazole, (C) base oil, and optionally (D) one or more additives selected from the group including antioxidants, dispersants, detergents, anti-wear additives, extreme pressure additives, friction modifiers, rust inhibitors, corrosion inhibitors, seal swell agents, anti-foaming agents, pour point depressants and viscosity index modifiers.