Experimental tests were performed on the OH-58A helicopter main-rotor transmission in the NASA Lewis 500-hp helicopter transmission test stand. The testing was part of a joint Navy/NASA/Army lubrication program. The objectives of the joint program are to develop and demonstrate a separate lubricant for gearboxes with improved performance in life and load-carrying capacity. The goal of these experiments was to develop a testing procedure to fail certain transmission components using a MIL-L-23699 based reference oil and then to run identical tests with improved lubricants and demonstrate improved performance. The tests were directed at components that failed due to marginal lubrication from Navy field experience. These failures included mast shaft bearing micropitting, sun gear and planet bearing fatigue, and spiral bevel gear scoring. A variety of tests were performed and over 900 hr of total run time accumulated for these tests. Some success was achieved in developing a testing procedure to produce sun gear and planet bearing fatigue failures. Only marginal success was achieved in producing mast shaft bearing micropitting and spiral bevel gear scoring.