What was found
DURING APPROACH, WITH SLATS & FLAPS 22'EXT, OBSERVED LEVEL 2 "SLAT DISAGREE". IAW QRH, RETURNED FLAPS/SLATS TO 15'/EXT. OBSERVED INTERMITTENT LEVEL 2 "SLAT DISAGREE". COMPLIED WITH QRH, PERFORMED FLAPS 22' /RET LANDING, EMERGENCY DECLARED. UNEVENTFUL LANDING (NO UNCONTROLABLE ROLL AT ANY TIME. PITCH, POWER, A/S ALL NORMAL DURING ALERT. INSPECTED SENSOR R4B AND FOUND SENSOR AND TARGET VERY DIRTY. CLEANED SENSOR AND TARGET AREA AND SHOOK WIRES, NO ALERTS SHOWN. CYCLED SLATS/FLAPS FULL TRAVEL NUMEROUS TIMES STOPPING AT ALL POSITIONS. ALL INDICATIONS NORMAL ON CONFIG PAGE, PFD'S AND PSEU SENSOR READOUT. PERFORMED SLAT POSITION INDICATION ADJUSTMENT/TEST IAW MM 27-84-00-5. ALL INDICATIONS NORMAL. AIRCRAFT OK FOR SERVICE.