As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
GREEN SYSTEM HYDRAULIC LOW LEVEL MAP LIGHT ILLUMINATED AT 22,000 FT WHILE EN ROUTE TO ACV. RESERVOIR PRESSURE WAS DECREASING AND ELECTRIC PUMP TURNED OFF. RETURNED TO SFO AND USED FREE FALL LANDING GEAR EXTENSION. REPLACED O-RING ON GREEN SYSTEM HYDRAULIC RESERVOIR TO HYDRAULIC BAY FORWARD BULKHEAD PRESSURE LINE FITTING AT RESERVOIR. RAN ENGINE, NO LEAKS NOTED.