As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
A/C HAD AN AIR TURNBACK TO BAH DUE TO LEFT DUCT LEAK LIGHT ILLUM EICAS MSG LEFT BLEED DUCT LEAK DISPLAYED LIGHT EXTIN AFTER ENGINE BLEED AIR SUPPLY AND ISOLATION VALVES CLOSED. FOUND LEFT ISOLATION BYPASS CHECK VALVE FLOATING SLEEVE LEAKING. REMOVED AND REPLACED 2 EACH SEALS AS PER MM 36-11-05, OPS CHECK GOOD.