Train undershoot WDL2 in AM by 1m due tointermittent BCU fault at Front M1 car. TC perform brake st atus check - fault self cleared. ~~~~~ #1689 When 750VDC cut off, B1 to coast having stuck brake. Found heavy air leak from solenoid coarse exhaust. Replaced ACU and carried out function test-ok. ACU-Old s/n: 1549-221  New s/n: 1541-182. Not: 2139310 Raise to RSW.    Done by Jack  09/03/20.