I don't know about NJ, I've never practiced law in the Garden State. But I can tell you, as a prosecutor, if someone brought me one seed, and the guy had bought the car used in the last twelve months, I wouldn't waste the tax payer's money because there's no way Blue State, that you are going to convince twelve people that the individual "knowingly" possessed, unless the cop also can testify the perp reeked of MJ smoke etc.
As a side note, if you buy a used car, many police stations will run their drug dog through it as a courtesy.