What was found
FLT 1157 - MKE-MSN - SHORTLY AFTER TAKEOFF, THE FLIGHT CREW NOTICED A SLIGHT SMOKE HAZE IN THE COCKPIT. DECLARED AN EMERGENCY AND RETURNED TO MKE. AFTER MAKING AN UNEVENTFUL LANDING MAINTENANCE INSPECTED THE A/C. AFTER TESTING ALL SYSTEMS FOR PROPER OPERATION. FOUND OIL IN THE RT ENGINE PRECOOLER. THE OIL WAS BELIEVED TO HAVE LEAKED INTO THE PRECOOLER WHILE REMOVED FROM THE A/C THE PREVIOUS NIGHT DURING A SCHEDULED INSPECTION. THE PRECOOLER AND THE PRECOOLER BYPASS VALVE WERE CHANGED DUE TO OIL CONTAMINATION. AFTER THE A/C WAS EXTENSIVELY RAN, IT WAS RETURNED TO SERVICE. (M)