What was found
SEA - ON DESCENT AT 10,000 FT STARTED APU, 10 TO 15 SECONDS AFTER INITIAL START TGT HUNG AT ABOUT 400 DEG, UPON TURNING APU MAIN SWITCH OFF APU FIRE LIGHT ILLUMINATED AND EXTINGUISHER LIGHT CAME ON. WENT THROUGH APU FIRE CHECKLIST AND LANDED WITHOUT INCIDENT. MX INSPECTED AND FOUND NO SIGN OF FIRE OR HEAT DAMAGE. THE APU ENG FIRE SENSING ELEMENT WAS FOUND BENT AND NEARLY TOUCHING THE COMBUSTION SECTION CASING. STRAIGHTENED SENSE ELEMENT TO ORIGINAL CONTOUR. TESTED IN ACCORDANCE WITH MANUAL, RAN APU CHECKED FOR LEAKS, ALL FUNCTIONS NORMAL. REPLACED APU FIRE EXTINGUISHER CONTAINER, VALVE AND CARTRIDGE. ALSO REPLACED DISCHARGE INDICATOR THE DISCHARGE LINE (TO THE INDICATOR).