As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
GENERAL HYDRAULIC SYSTEM FLUID QUANTITY BEGAN DECREASING IN FLIGHT. ACCOMPLISHED HYDRAULIC PRESSURE OR FLUID LOSS CHECKLIST. DURING APPROACH WITH AUX PUMP ON, QUANTITY STOPPED DECREASING HALFWAY BETWEEN FULL AND STANDPIPE. NO FURTHER FLUID LOSS WAS NOTED. REPLACED LEFT AILERON HYDRAULIC SYSTEM FILTER O-RINGS IAW DC8 MM CHAPTER 29. DURING ENGINE GROUND RUN, LEAK CHECK WAS GOOD.