If you have a hydraulic clutch and its slipping do you need to replace it?

Typically, yes. When a clutch engages it is the result of the springs of the pressure plate pinching the clutch plate into the flywheel. Anything that results in less pressure against the clutch plate will result in slipping. A worn damaged plate spring can end up creating less pressure. A worn clutch plate will not be as thick resulting in less pressure.

Slipping can also be caused by oil that may have leaked onto the clutch plate.

Unfortunately, the only way you can determine the cause of the problem will be to remove either the transmission or the engine so that you can examine the clutch assembly.