ACFT DAMAGED DURING LNDG PRACTICE.

Narrative

WE WERE ON A TRAINING FLT. AFTER SEVERAL TOUCH AND GOES; THE LAST LNDG WAS FIRM; BUT NOT HARD. WE PROCEEDED TO THE RAMP AREA AND SHUT DOWN. AFTER SHUTDOWN; I NOTICED FUEL WAS LEAKING FROM THE R ENG. SINCE THE ENG WAS HOT; WE CALLED THE CRASH TRUCK TO PREVENT ANY FIRE. THE GASCOLATOR BOWL CAME LOOSE. WE REINSTALLED THE BOWL. LATER ON; WE NOTICED THERE WAS SOME WRINKLED SKIN ON THE ACFT. UPON FURTHER INSPECTION; WE FOUND 5 RIVETS THAT HAD PREVIOUSLY BEEN POPPED (BECAUSE YOU COULD TELL THEY HAD BEEN RUBBING). I HAD THE STUDENT PREFLT IT BECAUSE I WAS ON ANOTHER FLT. I FIRMLY BELIEVE THAT THE ACFT WAS ALREADY DAMAGED OR WEAKENED FROM PREVIOUS TRAINING. THE ACFT WAS JUST 50 HRS OUT OF AN ANNUAL; BUT WE WERE HAVING A LOT OF TROUBLE WITH IT. THE MECHS MAY HAVE LET SOMETHING GO OR NOT HAVE CAUGHT IT. THE OWNER WAS NOTIFIED THAT EVENING. NO ACCIDENT/INCIDENT RPT WAS FILED IMMEDIATELY AFTERWARD BECAUSE IT WAS JUST SOME WRINKLED SKIN. BEING AN MEII FOR 2 YRS; I FEEL VERY STRONGLY THAT THE ACFT WAS ALREADY DAMAGED OR WEAKENED BECAUSE THE LNDG WASN'T A HARD LNDG. BEING THE INSTRUCTOR; I SHOULD HAVE PREFLTED THE ACFT. THE RIPPLED SKIN COULD HAVE ALREADY BEEN THERE AND WE JUST TOOK THE BLAME.