The most important failure mode of the HST gyros is flex lead rupture,caused by corrosion.This mechanism is characterized by a failure rate that is initially vanishingly low,and rises to large values only after a threshold time (determined mainly by the corrosion rate and not the initial strength of the flex leads) is passed.The threshhold time is a random variable,and so the failure time is also a random variable.The observed five times-to-fracture and the eleven observed operating times with no fracture,among the sixteen gyros to operate so far,are well fit using a Weibull Probability Law with time- scale n = 5.89 yr.and shape-parameter B =4.82: the correlation coefficient is r =0.989. This fit excludes the previously used Exponential Probability Law with better than 95% confidence.The total Probability Law for the lifetime of an HST gyro is the product of the Weibull Law for corrosion-induced rupture,with an Exponential Probability Law describing the other failure modes (electronic failure and lube patch failure)and an estimate of the latter;s mean-time-to-failure is roughly 28 yr.