Redarc dual battery system

I have just purchased a new aux battery that runs from my redarc dual isolator system.
Seems the solenoid has stopped working and that is what caused the battery to fail.
No charging for some time resulted in almost complete discharge without me knowing.
The unit is just over two years old and therefore out of warranty. New one is about $130.00 or so, too much for my current budget.
My question is this. Is the solenoid much the same as a continuous use solenoid similar to the starting type (short time use only). Checking on the wiring it looks like the black box simply supplys power to the solenoid coil when the voltage triggers the control box.
Has anyone tried to replace the solenoid with another cheaper version?

Pooley