The valve that you use to raise and lower the seat needs to be rebuilt. Often, when in the process you will want to rebuild the whole seat which includes rebushing the pivots and putting new o rings in the cylinder. Easiest by taking off the back and seat and removing the base from the tractor so you can turn it upside down and work on the parts.The small cylinder on the hydraulic ram is what provides the cushion or bounce so don't neglect to check and service that at your dealer.... Good luck