Concur with get a new Main Sensor.
If it is the miniclik from Hunter and I think it is.
Buy the whole unit, but unhook the cork like material in the cylinder by rotating the cylinder off. Put the new cylinder on the old rain sensor. You are done.
It will take you 1 minute to get the ladder, 30 seconds to get the old cylinder off, 30 seconds to put the new one on.
You are done.
Estimate cost retail 25.00.
Just do it.