Train EB was applied at track circuit S512 in Auto mode with Obstructed Motion Detected. Released EB- ok. Proceeded in ATPM mode to next station. ~~~~~ Train EB was applied at track circuit S5        Download and check from ER confirmed EB after 9 sec due to brake.Found #2502 brakes slow release at time of EB.Found hissing sound from ACU.Replaced ACU and brake static test done-ok.Brake function test brake able to release within 3 sec-ok.To be monitored on M/L. ACU:- New s/n: 1032/043 Old s/n: 1047/085 Not: 2428573 raise. Done by Ashwin/Arthur  20/10/22