What was found
(CAN) AFTER DEPARTURE, PASSING LEVEL OFF ALTITUDE, SELECTING FLAP TO ZERO, FLAP POWER CAUTION LIGHT ILLUMINATED AND FLAPS REMAINED A 10. REMAINED VISUAL AND GOT CLEARED TO RETURN TO BASE. REMAINED OVERHEAD AND RAN QRH 10.12, DICTATING A FLAP RESET. AFTER ACTIONING, FLAPS RETRACTED AND CLEARANCE WAS GAINED TO CONTINUE TO NEXT BASE. INTERROGATED CDS, FOUND HYD PRESSURE LOSS MESSAGE, CARRIED OUT FIM 29-10-00-810-803. BLEED NR 1 HYD SYSTEM ONLY, FOUND AIR IN THE SYSTEM, AIR REMOVED IAW AMM 29-10-00 SUBSEQUENT FLAP POWER CAUTION LIGHT AGAIN ILLUMINATED WITH SELECTION OF FLAP 10 FOLLOWED BY QRH ACTION. ON 10/09/13, THE FLAP POWER UNIT WAS REPLACED IAW AMM 27-52-01 AND OPERATION CHECKED SATISFACTORY IAW AMM 27-52-00.