What was found
IN CRUISE AT FL310, THE NR 1 ENGINE OIL QUANTITY STARTED DECREASING RAPIDLY. THE FLIGHT DIVERTED TO MKE. APPROXIMATELY 10 MINUTES PRIOR TO LANDING, THE OIL QUANTITY INDICATED 2 QUARTS AND OIL PRESSURE BEGAN TO DETERIORATE. A PRECAUTIONARY SHUTDOWN WAS PERFORMED, THE FLIGHT LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED THE ENGINE. ENGINE SYSTEMS CHECKED OK. AIRCRAFT RETURNED TO SERVICE.