As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
UPON REMOVAL OF GPS ANTENNA FROM AIRCRAFT, THE MATING SURFACE OF THE ANTENNA TO THE AIRCRAFT WAS RUSTING, CAUSING THE AIRCRAFT SKIN TO CORRODE. SUSPECT A VOID IN THE SEALANT AROUND BASE CAUSED MOISTURE TO GET UNDER ANTENNA AND CAUSE CORROSION. RECOMMEND CLOSE ATTENTION TO SEALANT BEAD TO ENSURE NO MOISTURE ENTRAPMENT. ANTENNA WAS REPLACED DUE TO SEVERITY OF RUST ON BOTTOM SURFACE.