I'm looking at a 91 turbo hard top which appears to be in perfect condition. It has about 113k miles on it.The only problem with the car (according to the owner) is that the "header gasket" is bad and this is causing the car to knock. He says as soon as the header gasket is replaced the knocking should go away. He insists that the header gasket is not the head gasket. I'm not familiar with MR2's so I don't know if he is being honest with me or not. Has anyone heard of the "header gasket" and could it be the source of the knocking?