 They did receive some improvements in the late 1950s with water cooling of the turbo-superchargers replacing the air-cooled units.In August 1974, 4301 was taken into Chullora Workshops for a regular overhaul, however a decision was made to use it as spares for the remaining units.The last was withdrawn in October 1979 with 4306 placed by the Public Transport Commission in the custody of the NSW Rail Museum.