As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT FL 400 THE HYDRAULIC VOLUME LOW -A- CAME ON. THE HYDRAULIC -A- QUANTITY GAUGE WAS SHOWING 12 PERCENT AND NORMAL PRESSURE. UPON LANDING THE QUANTITY WAS DOWN TO 10 PERCENT. REMOVED AND REPLACED LEFT ENGINE DRIVEN HYDRAULIC PUMP, LEAK AND OPERATIONALLY CHECKS GOOD IAW CE750 M/M 29-10-02..