Sorry it took so long to reply. I have a 2002 Montana with the same hydraulic unit. It sounds like the solenoid might be sticking but there is a strong spring inside that could be getting weak. I also think it could be your wall switch that could be causing the problem. I am trying to think of a good way to test it. You might try a spray of WD-40 on the back of the switch to see if it sticking.
My solenoid is located behind the hydraulic pump unit on that shelf. It is not easy to get at though.
