If you have the ARB 180103 Solenoid's you can service them yourself.
The procedure for dismantling the solenoid valve is as follows:
1. Unscrew and remove the top nut
2. Lift coil body
3. Remove screws from retainer plate
4. Pull to remove the retainer plate, tube and plunger
5. The valve can now be cleaned and serviced, making sure the bottom of the plunger and its seat in the body are in good condition
6. Reassemble as above
A fast "on the trail" fix for a malfunctioning solenoid is to dismantle the solenoid as above but remove the return spring from the plunger and reassemble without it. This will allow the Air Locker to engage but it won't be possible to disengage.