Gregory then began to wind down his motor racing career, continuing to compete in international sports car races with some good results including a second-place finish at the 1966 1000 km race at Monza alongside John Whitmore . Following his good friend Jo Bonnier 's death at the 1972 Le Mans race, Gregory stopped racing, and retired to Amsterdam, where he worked as a diamond merchant before operating a glassware business. On November 8, 1985, Gregory died in his sleep of a heart attack at his winter home in Porto Ercole, Italy. He had four children, Masten Jr., Debbie, Scott and Michael. Gregory was inducted into the Missouri Sports Hall of Fame in 2005 and the Kansas City . (Central Auto Racing Boosters) Hall of Fame in 2007.