Humidifiers and Dehumidifiers - Honeywell Solenoid Stuck in ON Position

My whole house humidifier has a Honeywell 32001639-002 Solenoid valve that is stuck in the ON position after about years of reliable service. This same thing happened to a previous unit (same model) which were both professionally installed. The previous unit was essentially gummed up due to the hard water in my area, so I am assuming the same for the current unit. I have both the old and current units, so I thought I would try to clean out the old one and see if that fixed the problem. Is it possible to use a cleaning solvent on this unit (like CLR) to dissolve the buildup and then reinstall? Will that destroy the components? Please recommend. Again, I have the old unit, so no harm done if I ruin it.

YOu can try the CLR on it, take the coil part of it off and soak it up, and see what happens.