It was a different time in 1974, when Master Gunnery Sgt. D. Michael Ressler joined the Marine Corps. President Richard Nixon was about to resign, Commandant Gen. Robert Cushman had recently overseen the Corps’ withdrawal from Vietnam, and Hank Aaron had just become baseball’s all-time home run king. Thirty-nine years later, Ressler will leave the Corps this month with more time on active-duty than any other enlisted Marine. A member of the “President’s Own” U.S. Marine Band, he will be honored in a retirement ceremony at Marine Barracks Washington on Friday, and officially retire Aug. 31. He served under 11…