Commercial-Off-The-Shelf (COTS) software components, component-based software, reused software, and object-oriented software come from diverse sources and have varied characteristics but can be integrated to form software systems. The L-metric, a metric with a very strong validation from its foundation in information theory, can measure the complexity of the interaction of such components. This paper briefly reviews some message basics and presents the L-metric. This paper looks at the sensitivity of the L-metric re four factors: 1 mdash; the amount of components such as COTS software incorporated in the system; 2 mdash; the choice of maintainer, 3 mdash; the extent of the customization of (COTS) components such as by wrappers and in-component changes; and 4 mdash; the effects of technology changes. In summary, the sensitivity of the L-metric can help in assessing in the face of software modification, the changes in system complexity affecting maintainability for systems with component software such as COTS.