It's the valve in the rear of the car that controls the hieght of the car. Assuming nothing else is leaking...

It's a one day project and you can get a rebuild kit from Phil, it a messy job but not techically difficult and takes about a day.

http://www.peachparts.com/shopforum/showthread.php?t=54894&highlight=rebuilding+wagon

I have seen another post on rebuilding it that I used, but I can't seem to find it.

Mine did the samething until I fixed...