a standard rebuild is still providing a repair beyond the level of the original part , the engine in a skylines done 50000 - 100000km and a have a fair amount of wear on them , the dealer is quite within his rights to provide a similar 2nd hand engine
if your talking about the aftersales warranties sold at an extra cost like all states then you will find their claims are all limited to a certain amount , a few thousand dollars usually . The dealer also has to provide a statutory dealers warranty , which is not cost limited which in most states is 3 months / 5000km . On top of that the dealer has to comply with fair trading legislation which gives implied warranties which are not cost or time limited . So its in the dealers interest not to sell f**ked engines even if he is selling aftermarket warranties with the cars.
even if you have one of these aftermarket warranties you are totally within your rights to make the dealer fix something under the fair trading statutes or the dealers warranty . once that expires use your own warranty
some dealers are dodgy and will try and avoid their obligations , but the law is always on the consumers side . you just have to enforce it