What was found
GYR - DURING C10 CHECK, DISCOVERED GROOVES WORN INTO PREVIOUS REPAIR DOUBLER ON THE LOWER SURFACE OF THE T/E WEDGE SKIN, FOR THE NR 4 LEADING EDGE SLAT. DAMAGE WAS CAUSED BY CONTACT WITH FIXED LEADING EDGE DURING EXTENSION AND RETRACTION. MAINTENANCE REMOVED THE EXISTING REPAIR DOUBLER AND FABRICATED REPLACEMENT DOUBLER IAW BOEING 757-200 SRM 51-70-10-2R. INSTALLED FABRICATED REPAIR DOUBLER AT WS 390L, ON THE NR 4 LEADING EDGE SLAT IAW BOEING 757-200 SRM 51-70-10-2R PAR 15, 18, 20 AND 21.