An auxiliary elastomeric sealing adaptor is disclosed which effectively provides a high degree of sealing, and prevents fuel leakage, between the metering valve stem and the tool stem components of a fuel-cell powered fastener-driving tool despite bending, tilting, or pivotal movements of the metering valve stem attendant a fastener-firing operation. In addition, the incorporation of the elastomeric adaptor between the stem components reduces the need for high tolerance manufacturing techniques and also enhances the service lives of the stem components. The sealing adaptor is mounted upon the free or distal end portion of the metering valve stem and is seated within a counterbored region of the fastener-driving tool stem. |