As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
HYDRAULIC LEAK. LEFT QUANTITY WAS .46. OCCURRED AT FL 330. RETURNED TO DEPARTURE. FOUND DIFFERENTIAL PRESSURE INDICATOR TO BE LEAKING ON NR 1 ENGINE DRIVEN PUMP PRESSURE CASE DRAIN FILTER MODULE, REMOVED AND REPLACED THE DIFFERENTIAL PRESSURE INDICATOR. OPS AND LEAK CHECKED OK.