It's that resistor? Did it get damaged mechanically by the movement of the whistle lever? You probably could replace that with a different power resistor, given the room. What size is it? Try measuring what is left of it. I see that Brasseur's has some 1044 parts, but no resistor.
http://www.brasseurelectrictra...lionel/720to1600.php
It's part number is Lionel 1044-56 and Olsen's Train Parts shows it for .25 from Lionel back in the day, but I don't know if they really have them and if so, what the real price would be.