As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SERVO WAS REMOVED FOR HOWLING NOISE IN FLIGHT, UNIT WAS DISASSEMBLED FOR OVERHAUL AND PN 41002521 COVER TO RETAIN VALVE, ID CORRODED AND VALVE SPRING WAS RUSTED IN HALF. IF RETAINER FAILED THE SERVO WOULD GO INTO BYPASS AND POSSIBLE HARDOVER CONDITION. COVER NEEDS TO BE MODIFIED TO ALLOW WATER TO DRAIN OR A BETTER BOOT NOT TO ALLOW WATER TO ENTER VALVE.