Ok, I'll tackle this one. I've got some experience with cleaning leather upholstery (not in vehicles, but in homes) and Leathermaster is a good product.
Vital is the conditioner. You need to apply the cleaner first. Couple different ways to do this...general best practice is to create a dry foam in some manner, apply it to the leather, work it in with a soft brush or sea sponge, and then wipe off. Using a steamer will provide far better results, but don't use a clothing steamer from Lowe's. You need one that puts out some serious, actual, steam. The clothing steamers tend to generate a lot of hot water that comes out with the steam, and you want as little of that in your leather as possible. I've got a steamer I paid $800 for, and it's at the beginning of what I consider acceptable for this sort of thing. You can get upwards of $3k pretty quickly on these things, but they've got a lot more productivity and versatility in that price range.
If the leather has picked up and is showing noticeable grease spots on the headrest, armrest, places like that...forgive me, but YOU'RE not going to be able to do anything about it. Hell, I can't even do anything about that, yet. The leather restoration class I want, taught by the guy I want to teach me, is ridiculous amounts of money. There's some videos online where some dude is drawing the oil out of the leather with naptha, but I REALLY don't recommend that. You've got to re-dye the leather afterwards, too.
To the OP: What the hell are you doing with aniline in a vehicle!? Holy cow, friend...you love your truck! Find a professional who can restore it properly, and then steam the leather every 3 months and apply both conditioner AND a protectant afterwards. Otherwise you're going to have to deal with the oil spots.
Hope this helped.
