There is a fellow on this forum who rebuilds them very reasonably, but I can't seem to find his name with the search function right now. ALso check this link
http://www.peachparts.com/shopforum/sl-forum/326888-129-top-hydraulics.html
Do the cyclinders leak? What is the actual problem? The electronic control module is notorious for getting out of sync and causing the top to not function. It can be reset. Is the red top operation switch flashing?
We can help if you give more detailed info.