I tried this to replace some severe damage. It didn't fix it, but the top layer of the leather had been scraped off.
Originally Posted by bengal-stripe
Take a generous dollop of shoe cream (the soft stuff that comes in glass jars) and put it on the damaged spot. Then take a metal tea spoon, hold by the handle and plunge your thumb into the bowl for greater pressure. With the back of the spoon you go in circular movements over the damaged area, using the shoe cream as a lubricant. (It's rather like a child playing with mud.)
Do that for about five minutes, then take the excessive shoe cream off and polish with a brush. In principle you are doing the same as was done in the tannery, rubbing fats deep into the leather and creating the top surface through pressure.
I can't tell you whether it will make the damage totally disappear, but it certainly will make it much better.