My mother's father (last name Leban) remembers a grandfather (possibly great-grandfather) that fought against Napoleon's army and would have had the "Leban" surname, so it would be in the Tolmin area before Napoleon.
"Leban" is a very common surname in the Tolmin area, my grandfather and grandmother both had the same last name, but the families thought each other to be unrelated, and with Slovenians, that means any relation would have been long before Napoleon.
My grandfather's father thought his family came to Slovenia from Germany seeking work in the mines - that does not mean anyone from Germany would have the Leban surname, but my grandfather believed it means "life" in German, and was a common surname. I know it is not common outside Tolmin, and that is the problem I have with anyone who says it is French, English, etc.
As I said, lots of people in this area have the surname "Leban" but it is uncommon outside this area. My own theory is a lot of unrelated people did not have a surname (or did not want to be known by it - for example association with the Rebellion) and started using "Leban".