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Any quality leather conditioner, such as Lexol, will work fine. As long as it does not have a dye it can be used on the KR leather. Even ordering from the KR shop you'd be overpaying, anything that has the running W brand on it is marked up about 50%.
I use neatsfoot oil which is in your lexol products. You can get either darkening or non-darkening formulations. Either will work, I have used both on my truck and on my saddles(2 out of the 3 are also King Ranch made) and I have not had a lick of problems out of either one(and I have been putting that stuff on one of my king ranch saddles for almost 20 yrs(grandfather's saddle, still use it to break the young horses)). Most people don't like it to darken the seats(I however, do although neatsfoot doesn't darken it that much, but it will darken it) so they tell you to stick with the non-darkening formula, you have to realize that you will need more of the non-darkening to condition the seats per time then you would of the darkening formula(due to the different formulation). Lexol is a good modest priced conditioner, you can get stuff from your local saddle shop that would be more along the lines of "generic", but they will be good as well. I can tell you that KR stuff is overpriced, got my saddles at a discount(pays to have a grandmother that went to grade school with the master saddlemaker), so I would stick with Lexol, however, they will both work.
On the advice of Dusty Johnson, who has been a saddle-maker for decades, I used Leather Therapy www.leathertherapy.com
My front seats had been cleaned by the dealrer with some sort of solvent and a pot-scrubber sponge and they looked very light and felt very dry. Used the leather therapy and they look GORGEOUS, feel supple and nothing rubs off. Love it!