As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SURFACE CORROSION ON SKIN I/B OF AFT HEATED DRAIN MAST ON LOWER FUSELAGE MARKED WITH DOT. GROUNDED - YES. REMOVED DAMAGE ON SKIN I/B OF AFT HEATED DRAIN MAST ON LOWER FUSELAGE FOUND TO BE IN LIMITS IAW B737-800 SRM 53-00-01-1A-5.W= 1" O= .063 R= .060 L= 1 1/2" D= .003.