A rubber composition contains an antifoam compound that leaches out of the rubber composition when placed in contact with a functional fluid. The antifoam compound is delivered into a functional fluid such as an automatic transmission fluid or an engine oil by contacting the functional fluid with the rubber composition. In addition to the antifoam compound, the rubber composition contains one or more elastomers, which may be selected from a wide variety of natural or synthetic rubbers. In a preferred embodiment, the elastomer comprises a high temperature elastomer such as acrylic elastomer and ethylene acrylic elastomer.