What was found
THE APU FIRE WARNING LIGHT ILLUMINATED WHILE EN ROUTE. THE APU FIRE BOTTLE WAS DISCHARGED AND THE LIGHT EXTINGUISHED. THE AIRCRAFT WAS DIVERTED TO AUS WHERE IT LANDED WITHOUT INCIDENT. MAINTENANCE FOUND THAT THE ELEVATOR PCU WAS LEAKING FLUID WHICH THEN DRIPPED ONTO FIRE LOOP OF APU EXHAUST DUCT. THE PCU WAS REPAIRED, APU FIRE EXTINGUISHING AND DETECTION SYSTEM WAS PLACARDED INOPERATIVE PENDING REPLACEMENT OF FIRE BOTTLE AND FIRE DETECTION ELEMENT DUE TO CONTAMINATION.