As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMBOUT AT FL280, RECEIVED HYD Y RSVR LO LVL MESSAGE. AN EMERGENCY WAS DECLARED AND THE AIRCRAFT RETURNED TO MCO AND LANDED WITHOUT INCIDENT WITH EMERGENCY EQUIPMENT STANDING BY. MAINTENANCE REPLACED AN 'O' RING ON THE HYDRAULIC POWER TRANSFER UNIT HYDRAULIC FITTING, SERVICED YELLOW HYDRAULIC SYSTEM RESERVOIR. LEAK AND OPERATIONAL CHECK OK.