I have releathered one of my SAs, replacing the X-series leather with one for the H-series, which is theoretically less stretchy. I weighed the two skins and they were within a couple grams, so guess the middle layer is a similar, less stretchy material. Feels the same riding.

Because the 2 series use Chicago screws and not rivets, this is a user-friendly process.

My sole Brooks is still rocklike by comparison, maybe time will change that.