Auto Finesse Leather Conditioner gives decent results and I've never had any problem with it staining but you do need to buff it after application to remove the residue. Have you thought about using a leather protectant coating?
Every few months I treat mine with Gtechniq L1 Leather Guard. It's a nano coating that protects and prevents staining, fading, loss and transfer of of colour/dye. It also creates a waterproof barrier so liquids just run or bead off. Was a god send when my child dropped a milkshake all over the back seat. Only problem was, it ran so beautifully off the leather, it ended up all over the carpet which was a mess
It's really good stuff imo, gives a nice matt finish, no nasty shininess. Before applying it I give the leather a good clean using either Auto Finesse Leather Cleaner or Dodo Juice Supernatural Leather Cleaner, both of which are good.
