As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE BS 1342, AFT CENTER CHANNEL (AT TOP OF FIREWALL) WAS FOUND SEVERELY RUSTED DURING A RE-ENGINE MODIFICATION. THIS CONDITION HAS BEEN FOUND ON ALL 38 A/C MODIFIED SO FAR. THE CONDITION IS PROBABLY CAUSED BY DISSIMILAR METAL AND LACK OF DRAINAGE. NOTE: THE RUST CANNOT BE SEEN WITHOUT REMOVING THE PART, SO IT MAY NEED AN X-RAY INSPECTION EVERY SO MANY YEARS.