RETURN LAND MANDATED BY A FLAP SLAT ASYMMETRY WARNING ON A B767-300 EICAS SYS AFTER TKOF FROM ZZZ.

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CAPT FLYING. BLOCKED OUT AT XA01Z. FLAPS 5 DEG TKOF INITIATED ON RWY 22L AT APPROX XA30. DEP CLRNC CALLED FOR A TURN TO 140 DEGS; MAINTAIN 5000 FT. FLAPS HELD IN POS 5 UNTIL APCHING HDG 140 DEGS; THEN FLAPS 1 DEG CALLED. APPROX 190-195 KTS; FLAPS UP REQUESTED. ABOUT 230-235 KTS; EICAS 'LEADING EDGE SLAT ASYMMETRY' ILLUMINATED; EXTINGUISHED; AND RE-ILLUMINATED. I DISCONNECTED AUTOTHROTTLE; RETARDED PWR; AND CALLED 'SPD 210 KTS.' AUTOTHROTTLE REENGAGED. MAX SPD OBSERVED WAS APPROX 245 KTS. FLAP LIMIT SPD IS 250 KTS. ACFT WAS LEVELED AT 6000 FT; AUTOPLT ENGAGED; AIRSPD 210 KTS. AT THIS POINT FOLLOWING CONDITIONS PRESENT: EICAS 'LEADING EDGE SLAT ASYMMETRY;' AMBER 'LEADING EDGE' LIGHT ILLUMINATED; FLAP POS INDICATOR (BOTH NEEDLES SYMMETRICAL) STUCK BTWN 1 AND 0. FLT MANUAL PROC 'LEADING EDGE SLAT ASYMMETRY (767)' PAGE 7-40 REVIEWED AND PARTLY COMPLETED. FO INITIATED PATCH TO DISPATCH AND MAINT CTL. THEY WERE BRIEFED AND ASKED ABOUT OUR ALTERNATIVES AT THIS POINT. MAINT CTLR SUGGESTED PLACING FLAP HANDLE TO 1; THEN 0. AT 1; FLAP POS INDICATOR JUMPED TO 0; BUT ALL LIGHTS STAYED ON. HANDLE RETURNED TO 0 WITH NO CHANGE. (PS: MANY RADIO DIFFICULTIES AT THIS POINT -- PATCH LOST 2 TIMES.) AT THIS POINT I DECIDED TO RETURN TO ZZZ. EMER DECLARED WITH ATC AND DISPATCH. #1 FLT ATTENDANT WAS CALLED TO COCKPIT; BRIEFED; AND 'CABIN ADVISORY' DECLARED. I MADE A BRIEF ANNOUNCEMENT TO THE PAX; EXPLAINING THE PROB; AND OUR INTENTIONS. SUBSEQUENTLY WE WERE CLRED FOR ILS RWY 27L; ZZZ. IRREGULAR PROC AGAIN REVIEWED AND COMPLETED IN ENTIRETY. FLAPS 20 DEGS. SPD 30 KTS REF +30 IN THIS CASE 160 KTS. TOUCHDOWN AT 160 KTS WITH AUTOBRAKES #2. NORMAL TOUCHDOWN AND ROLLOUT TO THE END. AFTER CLRING; RETURNED TO GATE WITH HOT BRAKES.