What was found
FLIGHT 2792 DURING THE CLIMBOUT THE CREW REPORTED AN EXHAUST TYPE ODOR IN THE COCKPIT. ODOR INTENSIFIED. BOTH COCKPIT CREW MEMBERS DONNED OXYGEN MASK & ELECTED TO RETURN TO DFW. PASSENGERS DID NOT REPORT DETECTING ANY EXHAUST ODORS. ACFT REMOVED FROM SERVICE. REMOVED AND REPLACED THE NR 1 ENGINE IAW AMM 71-00-00. OPERATIONAL CHECK GOOD AND PERFORMED ETN EM-72-034 R4 NO NOTICEABLE OIL ODORS IN ACFT. DURING SHOP VISIT THE PFI WAS DECLARED AS BEING THE 0 CARBON SEAL, HOWEVER ALL SEALS WERE LEAKING ON THE ENGINE. THE AIRCRAFT WAS RETURNED TO SERVICE.