I use the 303 upholestery cleaner as is. I do not dilute it. Though I have a feeling you are talking about the 303 all purpose cleaner that is dilutable. I have never used that product, so I can't help with dilution ratios.
You could just have a spray bottle of vinegar and water at 1:4 and sprintz a liitle on for rinsing. It works on carpeting, but I haven't tried the sprintzing on the leather seats.