In this paper, we study a manufacturing system with repair and rework. We show that in such systems the product quality, in terms of quality buy rate (the good job ratio of all jobs), can be described by a function of repair capacity and first time quality (the good job ratio of all first time processed jobs). Variations in first time quality can lead to reduction of quality buy rate and substantial waste of production capacity and materials. Therefore, the repair and rework system should be designed to be robust to the fluctuations. Moreover, we observe that the quality buy rate is practically independent of the distribution of the first time quality, but depends primarily on its coefficient of variations