Leaking gas tank filler tubes ?

I went over to my storage and compared the 64 tube to the 67 tube I have. I can't see a difference in the ID between the two. A baffel would work. My thought would be to use some foam, the same as used in aftermarket fuel cells at the end of the tube. The foam in the cells are used for preventing slosh. Why not use it for the same thing in your tube?.