If you don't have to send it back, I'll take it apart and try and find out what is wrong with it. Fix it if you can and save it. Are the new and the old one have the same size shaft?
I had a similar problem with my dump trailer. Manufacturer wanted $300+ for a new cylinder -- said that would fix the problem. Removed cylinder took it to my local hydraulic/bearing place, and they fixed it (found cylinder seized at certain points) with with new-style seals/pistons. Cost was about $75.
Wanted to pass that along for other that may have the same problem.