I have a black Soho leather swingpack that I have never treated or put anything on.
I bring it to trips all the time. Last December, during one of our sightseeing trips to NYC, we got caught in a huge, torrential downpour. I tried to shield my bag as much as possible but it still got soaked. I have to say that as scared as I was that my bag was ruined - after I patted it down with a towel and it dried out, it still looked great. No spots, no marks. I'm not sure if I just got lucky but I've been really impressed at how this swingpack has stood the test of time....and horrible weather!!