Our rig is a little older than yours so the parts might not be the same. Ours is a Spraying System #AB144-1-3 three way solenoid valve. I found parts from this source:
Farmchem Corporation Information
Order by phone and talk to a real person, otherwise shipping is about the same cost as the rebuild kit (about $15). If he knows that ahead of time, he can just drop in the mail because the kit isn't very large.
Our solenoid valve is located in the water compartment (driver's side) behind a white panel with several screws. When you get the panel off, you will see both the bypass valve and the winterizing valve. Have someone inside operate the switch and then work on the valve that clicks.
Disassembling the solenoid to replace the rubber parts is not difficult, just be sure to make reference marks to insure it goes back together the same way (don't ask me how I know).
Good Luck