In February 1979, four Stirling cycle cryogenic refrigerators, designed and built by Philips Laboratories for the Johns Hopkins University/Applied Physics Laboratory, were launched into orbit aboard a P78-1 spacecraft. These refrigerators, designed to cool two identical gamma-ray spectrometers for a Lockheed experiment, have been highly successful; they hold the record for in-orbit operation of any closed-cycle cryogenic refrigerator. The refrigerators are still in orbit and have individually accumulated from 4700 to over 20,000 hours of operation. The in-orbit performance of the units demonstrated both high reliability and the capability of exceeding their one year maintenance-free life. However, telemetry data indicated degradation in the refrigerator's operating temperature. Specifically, the Lockheed Palo Alto Research Laboratory experiments indicated a 0.4°K/day short-term increase in temperature and a 16°K increase per year. Although these increases were within acceptable limits, Philips Laboratories initiated efforts to eliminate or minimize the reported degradation. A refrigerator identical to those in orbit was built, with one significant modification: flexible metal bellows were introduced between the crankcase and the working volume to prevent possible contaminents from migrating into the latter. During the life test of the modified refrigerator, the temperature increase for the first three-month run was 0.022°K/day, a negligible level. The unit has accumulated 11,000 hours of operation as of June 1982.