Doesn't mean it's right. I am not familiar with that oil and the wrong oil can cause the clutch to slip.

Springs could be weak or adjusted wrong.
Throw out could be binding.
Discs could be worn or glazed.
Cable could be frayed and binding in the housing.

I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!