I had my vinyl seats redone by a great little one man upholstery shop nearby. Yes, I know, vinyl and not leather, but I wanted to remain as original as possible. He told me that he would give me a little secret. He recommended for all my vinyl material including the roof and touneau cover etc... Lexol, a leather treatment spray. I can get it at my local farm supplier.
http://www.southernstates.com/catalog/search.aspx?searchterm=lexol
It works well on vinyl, and I expect it works well on leather.

'67 +4 tourer - broken white - RHD