i just heard of a guy who's recently sold a supra and it was because the head gasket just kept going, 3 or 4 times...
it sounds as though the guy was doing something wrong. not torqueing it right or most likely the head was warped. when replacing the h/g its a good idea to get the head machined.
with a good h/g,machining and proper fitting, u should have no problems in the future...