I use the plastic from two large yogurt tubs with the top rim and bottom removed. Cut each one into a strip that is wider than the leather but will fit the slot, about 4". Use these to create a sandwich using the leather as the filling. These enable the leather to slide easily even when stiff. Push the free end up into the air channel and pull it thro. If the leather doesn't want to pull out the bottom side, sandwich them to help them slide. That old saddle had leathers that felt cemented around the tree. I had them out in less than 10 min. Same putting them back altho they'd been cleaned and oiled then.