What was found
(CAN) ON DEPARTURE ACFT WAS UNABLE TO RETRACT FLAPS. IN CONSULT WITH MOC AND BEING ADVISED THIS IS A REOCCURRING ISSUE A DIVERSION BACK WAS REQUIRED. CREW AND DISPATCH DETERMINED FLIGHT WOULD BE BETWEEN 3500-4000KGS OVER LANDING ON RWY. CREW ASKED FOR TRUCKS TO MEET ON RWY AND INSPECT BRAKES DUE TO OVERWEIGHT LANDING. NO EMERGENCY DECLARED WITH ATC. STRICTLY PRECAUTIONARY, RESOLUTION: FOUND PINS CORRODED AND BROKEN OFF IN LT OTBD SKEW SENSOR ON SLATS 2/3. LT SLAT SKEW SENSOR 2/3 REPLACED IAW AMM 27-83-01. LT OTBD SLAT SKEW SENSOR 2/3 HARNESS REPLACED IAW WDM 27-83-53, SHEET 2. OPS TEST CARRIED OUT IAW AMM 27-83-01-710-801, SERVICEABLE.