Your situation got me thinking. You bought a new in box from a Stern Athorized distributor. Your warranty just began even though the pin has been out of production for a while, right? You should be covered and not have to worry about any surprises.
However I guess the downside would be if you needed parts that are no longer available. But people restore really old pinball machines and get them up and running like new all the time. With your distributor and the manufacturer backing you there probably isn't anything that couldn't be made right.
Congrats on your new pin.