As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING #1 ENGINE START, NOTICED FUEL LEAKING FROM THE MAIN FUEL/OIL HEAT EXCHANGER. THE LEAKAGE RATE WAS A STEADY STREAM DURING INITIAL ENGINE START. AFTER ENGINE START IT WAS 5 DROPS A MINUTE. AFTER 5 MINUTES IDLE RUN ALL LEAKAGE STOPPED. GROUNDED - YES. REMOVED AND REPLACED #1 ENG MAIN OIL/FUEL HEAT EXCHANGER REF B737-800 AMM 79-21-02-000-801-F00 & AMM 79-21-02-400-801-F00. 5 MIN IDLE LK CK'D GOOD. NO LK'S NOTED.