TC reported BCU brake fault at car 2509.Train performance ok. ~~~~~ 2509 TC reported BCU brake fault. Train performance ok.  2509 performed brake cyclic test & D/L ER. Found #2509 brakes slow to release 3 times. Replaced the ACU & checked no air leakage. Performed brake cyclic test - OK.  Shafie/Sugu/Lee PT 44740