A fractional percentage of a silicone compound was inadvertently introduced in one lot of Rheolube synthetic hydrocarbon grease used in the spin bearings of our momentum control systems. As a result, a decision had to made in a very short time as to whether the grease would meet the performance and life requirements. To accomplish this, a series of tests were undertaken to compare the performance of the subject grease or oil extracted from it to compare to the baseline lubricant. These tests represented each phase of bearing life: vibration, beginning of life, normal operational life, and end of life. Included were two different wettability tests, two different types of elastohydrodynamic lubrication tests and two different types of boundary tests. Acceptance test data of existing units with and without the subject grease were also used to determine how operational performance was affected. In addition to this test data, the Honeywell/Hanks lubricant life model was used to conclude that the subject grease would support our requirements.