What was found
ON INITIAL CLIMB, AFTER FLAP RETRACTION, EICAS CAUTION MESSAGE OVHT ENG 1 NAC. COMPLIED WITH CHECKLIST AND MESSAGE CLEARED, TRIED TO CONTINUE WITH CLIMB, MESSAGE RETURNED. RETURN TO LAX. REMOVE AND REPLACE NR 1 ENGINE TWELVE SEGMENT LPT COOLING AIR MANIFOLD IAW AMM 75-24-03. SYSTEM OPS CHECK GOOD.