his career, his best being a sixth at the 1962 United States Grand Prix at Watkins Glen with the UDT Laystall team, in a Lotus 24. Running fourth, just behind eventual winner Dan Gurney at the French Grand Prix, Gregory retired with ignition problems, losing possibly his best chance at a maiden Grand Prix victory. Gregory did manage a win in the non-Championship 1962 Kanonloppet race at Karlskoga in Sweden, but this race did not feature any top teams. After Formula One After his release from Cooper, Gregory also went back to competing in sports car races, setting the overall fastest lap at the 1960 24 Hours of Le Mans. He won the 1961 1000 km Nürburgring, driving alongside Lloyd "Lucky" Casner in a Maserati Tipo 61 for the America Camoradi Racing Team. In the same year, Gregory finished fifth in the 24 Hours of Le Mans in a Porsche RS61 Spyder. 1962 saw Gregory win the Canadian Grand Prix sports car race at Mosport Park in a Lotus 19-Climax. In 1964, Gregory again competed in the 24 Hours of Le Mans, this time in a Ford GT40. He retired from the race in the fifth hour due to gearbox difficulties. The following year, Gregory teamed up with the man who was to become 1970 Formula One World Champion, Austrian Jochen Rindt, and the pair won the race in a North American Racing Team Ferrari 250 LM. 1965 was also the year in which Gregory raced in the Indianapolis 500, starting from the back of the grid and working his way up to 5th before being forced to retire due to an engine problem. 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, the Kansas City C.A.R.B. (Central Auto Racing Boosters) Hall of Fame in 2007 and