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I don't think it's going to matter at all but you my as well pay if it's only $400, Lenders are still going to see the loan rather paid off or not and further more wouldn't you be going back to Navy for the new loan or are you looking at something brand new that has 0%?
Your FICO score will likely not gain points as a result of paying it off, and since the loan balance is so small, I don't think that you really have anything to gain from paying it off early ~ unless it will save you some time/hassle when you are ready to negociate/purchase a new car.
Take the extra month on the car loan to pay it off (or two months depending on your installment amount).
I think any difference from a lender perspective is going to be utterly trivial, but the two extra months on the loan may have a small but statistically meaningful benefit to your credit score longer term.

It won't matter either way. It won't affect your AAoA, and you likely won't gain any points from paying it off (early doesn't matter at all). I'd pay it off just so you don't forget to, but it won't matter either way.