As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON DEPARTURE FROM MEM THE GREEN SYSTEM HYD LOW LEVEL LIGHT ILLUMINATED. THE PIC DECLARED AN EMERGENCY AND RETURNED TO MEM. A JAM NUT FOR THE O-RING ON A TEE FITTING COMING OUT OF THE MAIN HYD SYSTEM ACCUMULATOR WAS TIGHTENED AND LEAK CHECKED WITH NO LEAKS FOUND AND THE A/C RETURNED TO SERVICE.