What was found
DURING APPROACH WITH LANDING GEAR DOWN AND FLAPS 20/20, F/O GOT UNRELIABLE AIRSPEED ON PFD FOLLOWED BY SLATS/FLAPS SYS 1 AND 2 FAULT O/H. SLATS/FLAPS CYCLED PER QRH, THE LIGHT/FAULTS CLEARED CONFIGURED AGAIN THE SLATS STUCK AT 15 DEGREES. FOLLOWED QRH FOR SLATS STUCK LANDING. ON FINAL APPROACH FLAP HANDLE AT 40 DEGREES SLATS BROKE FREE AND WENT TO 30 DEGREES SLATS WITH 40 DEG FLAPS. THE LANDING WAS UNEVENTFUL. SLAT/FLAP RETRACT ON THE GROUND WAS NORMAL. CHECKED SLAT 0 POSITION AND INDEX OF LT APU, WW IPPU AND FPPU, CHK OK. REMOVED AND REPLACED RT APU ALL AMM 27-81-19-4. REMOVED AND REPLACED RT SLAT TORQUE LIMITER PER AMM 27-84-12-4. OPS CHECKED NORMAL PER AMM 27-84-00-5.