Here's the part number for the Suspension valve rebuild kit. 000-586-00-32 The kit is about $70 last time I bought one. And I could only find it at the dealer. I am going to check at work tomorrow to see if I can get one cheaper from the parts supplier we use at Grease Works.
Here's a write-up member lrg did a while back.
Wagon rear suspension valve rebuild
Make sure when you pull the valve apart you pay very close attention to how things come apart. There are several small springs, and parts that can fall out. Also pay attention to how the cam that is inside is oriented. It can go back in several different ways. But only one way is the correct way.

Also, here is a write-up I did on Diagnosing your Self-leveling system - http://www.schumanautomotive.com/forums/showthread.php?t=2226

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