What was found
ON APPROACH FOR LANDING AT ABOUT 200 KTS, THE YELLOW "SLAT DISAGREEMENT" LIGHT ILLUMINATED WHEN SLATS WERE SELECTED TO EXTEND. THE AIRCRAFT ALSO EXPERIENCED AN UNCOMMANDED ROLL TO THE RIGHT WHEN THE LEADING EDGE SLATS FAILED TO DEPLOY SYMMETRICALLY. AS THE AIRCRAFT SLOWED THROUGH 190 KTS AN AUDIBLE BANG WAS HEARD, BLUE "SLAT EXTEND" LIGHT CAME ON, AND THE "SLAT DISAGREEMENT" LIGHT EXTINGUISHED. LANDING WAS COMPLETED WITHOUT ANY FURTHER PROBLEM. MAINTENANCE INSPECTED THE SLAT SYSTEM BUT WAS UNABLE TO DUPLICATE THE FAULT OR TO FIND ANY PROBLEM AT ALL. THE T-DUCT O-RINGS AND SEALS WERE REPLACED PER MC DIRECTION. THE AIRCRAFT RETURNED TO SERVICE.