As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NEWLY INSTALLED FUEL FILTER O-RINGS LEAK CHECK OK DURING GROUND OPERATION, BUT BEGIN TO LEAK AFTER ABOUT AN HOUR FLIGHT TIME. WHEN THE SAME PN M25966/1-928 IS UTILIZED BY ANOTHER MFG, UTILIZING AN ASTM STANDARD FVMQ VS. THE PRECIX O-RING WITH A SPECIFICATION OF: AMS-R-25988. THE LEAK NO LONGER OCCURS.