What was found
ON APPROACH FROM CVG TO DTW CREW NOTED HYDRAULIC QUANTITY (YELLOW) WAS LOW, JUST BELOW 1/4. AT THE GATE F/A'S ADVISED CREW SMOKE AND FUMES IN CABIN. NOTED LEAK UNDER CABIN ON GROUND COMING FROM HYDRAULIC BAY. MAINTENANCE NOTED YELLOW HYDRAULIC SYSTEM PRESSURE TRANSDUCER HAS A BLOWN O-RING PROTRUDING FROM ITS ATTACHED FITTING, IT WAS NOTED THAT THE FITTING WAS TIGHT. MAINTENANCE REPLACED PRESSURE TRANSMITTER RDI CODE 1/DN2, CLEANED RESIDUAL FLUID, SERVICED, BLED HYDRAULICS. PERFORMED LEAK CHECK.