We have restored a 1998 - 763 and have an issue with the hydrostatic system. During restoration we rebuilt the drive motors. The gerollers looked good - no scratches at all and reasonably tight. However, it has low power on the left side. I've bought a guage and will pressure test both pump for reference. I'm assuming we will have to rebuild the hydrostatic pumps. My question is do I have to replace all of the pistons and swash plate if I find a worn piston? Or can I find just single pistons for sale? So far my internet serach only shows complete kits. I'm just trying to save the money and not replace good parts. Has anyone done this before. Thanks