I want to by a used cadillac. I was told the head gasket needs to be changed

look at the estimator price,top of this page!your vehicle info,your zip code,and work to be done!!

short answer is a big, fat NO! if you do know anything about cars. Do not do it by yourself. include cost of car repair into the price to get TOTAL price of the car if it running right. the car most likely has a "northstar" engine.