What was found
APU WAS STARTED ON FINAL AND UPON TOUCHDOWN, CREW RECEIVED AN APU FIRE WARNING BELL AND INDICATION LIGHT. AS AIRCRAFT CLEARED THE RUNWAY, CREW PULLED AND ROTATED THE APU FIRE HANDLE, DISCHARGING THE BOTTLE. FIRE LIGHT EXTINGUISHED AS CREW SWITCHED THE APU OFF. CREW ASKED TOWER IF THEY OBSERVED AND SMOKE. TOWER RESPONDED NO SMOKE WAS NOTED. FLIGHT TAXIED TO THE GATE WITHOUT FURTHER INCIDENT. NO EMERGENCY WAS DECLARED. MAINTENANCE FOUND THE APU TAILPIPE LOOSE AND SEAL DETERIORATED ON LOWER SHROUD EXHAUST OPENING. REMOVED AND REPLACED APU ASSEMBLY AND SEAL, ALSO, APU FIRE EXTINGUISHER AND YELLOW INDICATOR DISCHARGE DISC. OPERATIONAL CHECK AND LEAK CHECK GOOD.