ive been looking at an LT5 engine and trans that are for sale locally.the guy is telling me that this was a factory replacement LT5 and trans. that the dealer had replaced the original LT5 engine and trans under warranty at one point during the cars lifespan....the engine and trans do not have the serial numbers of the vehicle stamped into either part......is there some way to determine if these were replaced over the counter at a gm dealer?? certain serial number or engine trans codes???