What was found
(CAN) AFTER EXPERIENCING DC POWER DIFFICULTIES OVER SEVERAL TIMES, FURTHER INSPECTION REVEALED WATER STAINS ON TOP OF THE LT AFT POWER DISTRIBUTION PANEL (PDP). AFTER REMOVING THE PDP COVERS, WHITE POWDER ALUMINUM LIKE CORROSION WAS FOUND INSIDE THE COVERS. INTERNAL PCB HAD 2 LARGE CORROSION SPOTS OVER SEVERAL CONTACTS. FOUND DIRECTLY ON TOP OF THE LT AFT PDP WAS A MATING FLANGE FOR APU COOLING. THIS FLANGE WAS LEAKING WATER FROM RAIN AND FREQUENT AIRCRAFT WASHING. THE SEALING WAS FOUND TOO THIN ALL OVER THE FLANGE AND SEALING WAS COMPLETELY MISSING WHERE THE 4 RETAINING BOLTS WERE DUE TO FLIGHT VIBRATIONS OVER TIME. (TC NR 20060313001)