As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING A SCHEDULED INSPECTION, REPLACED A DUCT ASSY OFF OF THE HEAT EXCHANGER WITH AN IMPROVED DUCT ASSY. AT DISASSEMBLY, DISCOVERED THAT LT HEAT EXCHANGER HAD CRACKS FROM THE BOLT ATTACH POINTS. THE CRACKS WERE FROM .25 TO .75 IN LENGTH. IT APPEARS THE CRACKS ARE FROM ALL 4 CORNERS OF THE MOUNTING BACK PLATE ON THE HEAT EXCHANGER.