Go to powergearus.com
That has all kinds of information...and you might even be able to contact (e-mail or phone) a real live person.
If your jacks are sticking....spray some silicone on the chrome pistons at least 3-4 times a year.
I have a 2001 system (hydraulic) and just replaced (myself) one of the jacks. Over 600 bucks (new, from PowerGear). They won't sell you, but you have to buy thru a dealer or retailer. They are not exactly consumer (us) friendly.
My problem is this old, leaking jack might be able to get rebuilt. I cannot find any shop closer than 80 miles away that would even THINK about taking care of a rebuild....and if it cannot be rebuilt, I would have to pay them to take the thing apart and diagnose the problem. IF there is any kind of dings, scratches or imperfections on the chrome piston, forget any rebuild....for any kind of savings over a new one.
You can find used ones on the 'net for about $350....but would you trust that? Not I.......
If you want my story on buying and replacing, PM me.