To mark the difference: what you are describing as drawback would be repayment or remission under our own customs code, and the economics are identical. A specialist takes on multi-year exposure to a customs audit in exchange for a fee, and a claim this size does not clear that bar for anyone doing it professionally, on either side of the Atlantic. The size of the duty at stake is not what determines whether it is worth doing: the years of standing obligation afterward is.
