i would of told you to get RAC check aswell, but to be honest i think they just check cosmetics. MY mate bought a CA18 S13 and had it RAC checked first, after a few months he had leakin gaskets, corroded exhaust pipes, and the car was only running on 3 pistons. To me it seems like internals are what you would be most worried about as you cant check them yourself. so i dunno what the RAC check.
mind saying that i still wouldnt buy a car without having them check the stuff they do :S