I agree with JWL. Find the problem before try you fix it, and I wouldn't bend my bumper with the old up against the tree and "burn it in" trick! Does it use a lot of oil and not smoke? If it leaks enough to make the clutch slip there should be oil dripping around the bell housing. Do you know any history on the car, has the clutch been changed or is it being driven by an inexperienced driver? Does it have the proper amount of free play?
That's what I'd check before taking anything apart.........Mark