Properly protected              Iron corroded because the
    iron surface                         lubricant does not contain
                                                 a corrosion inhibitor

Corrosion occurs when water enters the lubricant system: this can be counteracted by the use of corrosion inhibitors. In addition, like the metal deactivators, they deactivate the metal surface thus ensuring that lubricant degradation processes are not catalyzed.  

Widely used corrosion inhibitors include:
Ciba® IRGACOR® L 12, Ciba® IRGACOR® L 17 for oil based fluids
Ciba® IRGACOR® L 190 PLUS and Ciba® IRGACOR® L 190 for water containing fluids