See my previous posts on this matter.  I went through the same waste of time with Dukes.  Maybe I should just start a business to test and repair these darn things.

$5,000 is a lot when it could be solenoid, seating, leak, controller or lines.   Can you isolate the problem further?  What kind of test tells you the valve is not moving?  Most of the problems I've seen are dirty seals which can be cleaned or worn seals that get replaced.