Redarc battery isolator ( dual battery ) Failure

Greetings guys - as the topic suggests - my REDARC duel battery isolator has failed - left the car radio on over night by accident - by morning - battery drained - not enough voltage to start car - so hit the momentary switch to get a jump from second battery - No distinct click from isolator - closer inspection and i see the control module looks like it swolen ( and cold so must have swolen over night due to voltage drop ???? )

anyway question is , is the controller module ( little black box ) available for sale ? or do i have to buy the whole isolator again ??

thanks

BB