Sounds like your csc was failing, your fluids were low or there was air in the system...
Should be warranty...
I'm not sure what they mean by the clutch being bad, but that doesn't have to mean it's just worn... You shouldn't be able to wear out a clutch in 12k with normal driving, so I'm guessing they meant something else.
Anyways I would make sure you get your old clutch back, so you can see what they mean with bad.
I wouldn't go aftermarket if the rest of your car is stock....
__________________
|