If the master or slave is leaking, then no..that mechanism only RELEASES the clutch..now if by some miracle it is sticking partially engaged, then yes it could cause a slip..check the arm that the slave pushes on. It should have a tiny bit of play in it at rest, just enough to jiggle it. If it is hard as a rock, then it could be holding the clutch slightly, but other than that its time for at least a new disk and pressure plate and a resurface.