I recently detailed my wife's Z4 M Coupe. Car needed some TLC. Full clay bar, 2 coats of Menzerna Power Lock. I also detailed the leather inside, and there is a lot of it on this car since it has factory Extended Leather. My favorite cleaner of all time is Swissvax nappa leather cleaner, with their little brush to work it in. I follow the cleaner with Spinneybeck conditioner, which I apply by hand like moisturizer on skin. I put on a thin coat, let it sit for a few minutes, then I blow it dry with a hair dryer. I don't buff it. The hair dryer helps the leather absorb all of the conditioner and leaves the leather feeling almost like velvet. Car is clean and ready to run.