A system for enhanced sealing against intrusion of moisture and other contaminants for medical/dental handpieces having rotating or other moving elements driven by a motor within the handpiece. The enhanced sealing includes tandem seals on stepped diameters to provide additional flow pathway impediments. The tandem seals preferably include spring seals that are positioned in opposite directions to provide enhanced sealing against pressures in two different directions that occur during the pressurization and vacuum cycles of an autoclaving process. Additional enhancements include the use of annular sealing rings with x-shaped cross sections.