Don't panic, you may not need a clutch rebuild.
First, make sure the hydraulic system is working properly. Air in the system and/or crud in the clutch cylinder can prevent the clutch from engaging fully. Try bleeding and flushing the system. If that doesn't do it, either the cylinder is malfunctioning or the clutch does need attention. Flushing may not remove all the junk from the clutch cylinder, so the next simplest thing to try is a clutch cylinder cleaning and rebuild. Be sure to check for a plugged return port.
If slipping persists, disassemble the clutch and measure the plates and springs. Replace as necessary. If the plates and springs meet specs, either the clutch cylinder is still malfunctioning and needs to be replaced, or possibly the clutch plates have been ruined by an oil additive.