What was found
ON PUSHBACK MEM AFTER DISCONNECT WITH A PUMPS ON, L/E FLAPS REMAINED UNSAFE. CYCLED FLAPS 2-5 DEGREES WENT GREEN. CYCLED FLAPS BACK UP, UNSAFE WENT OUT. PASSING 10K UNSAFE L/E FLAPS RE-ILLUMINATED. CYCLED DOWN AND BACK LIGHT WENT OUT. PASSING 19K, UNSAFE L/E FLAP RE-ILLUMINATED RETURNED TO MEM. LOWERING FLAPS FOR LANDING, L/E FLAP UNSAFE OUT SELECTING FLAPS 5. REMAINS UNSAFE FLAPS 2 OPERATED L/E SEVERAL TIMES. L/E FLAP LIGHT REMAINED LIT WHEN SLATS WERE UP. CHECKED LED PANEL AND CONFIRMED NR 4 SLAT NOT UP INDICATION. T/S PER WDM AND DETERMINED NR 4 SLAT ACT SW IS BAD. REMOVED AND REPLACED NR 4 SLAT ACT REF 727-200MM 27-81-032-4, OPS CHECKS GOOD AT THIS TIME.