As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LOST HYDRAULIC SYSTEM GREEN QUANTITY JUST PRIOR TO REACHING CRUISE ALTITUDE AIR TURN BACK. FOUND LEFT ENGINE CASE DRAIN FILTER ASSEMBLY TOP LINE B-NUT LOOSE. TIGHTENED PER AMM 29-11-43-400-804-A. RAN CHECK OF GREEN HYDRAULIC SYSTEM IAW AMM 29-00-00-280-006-A01. OPERATIONAL CHECK NORMAL. RAN LEFT ENGINE. ALL PRESSURES NORMAL. NO LEAKS NOTED. SERVICED GREEN HYDRAULIC SYSTEM IAW AMM 12-12-29-611-001-A.