As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INFLIGHT AT FL 350, HYDRAULIC QUANTITY SUDDENLY STARTED DESCENDING AND CONTINUED DESCENDING. ISOLATED HYDRAULIC SYSTEM. RETURNED TO MIAMI AND FOUND RUDDER SELECTOR VALVE PLUG LEAKING. REPLACED O-RING, NO LEAKS NOTED IAW DC-8 MM 29-00-00.