Making the leather is easy. Punch an oblong hole in a small rectangle and press it on. You trim it to the form fitting oval last, after all else is done.
I really wish Estwing leather handle hammers were more cherished by the tool public.
(Eddie made this hammer whatever name is on it)
To repair a leather handle effectively, especially when a substantial part of the leather is gone,
would require a custom clamp to do a good job.
I would endeavor to make said clamp, except repairing inexpensive yard sale hammers isn't likely to pay much.
If they were suddenly being scarfed up fast by collectors, at $250 apiece, I'd go for it.
yours Scott