I don't know what Audi used on their arm rests for A4s, but I just saw a '96 A4 with leather and the arm rest covering was cracked and split open like it was 20 years old.

Obviously that car never received any leather care.
IMO, different leathers require different care and products. I've got 2 pairs of
HS Trask shoes , one made out of bison leather and the other pair out of elk. I use HS Trask's Buffalo Butter on them and this stuff soaks right in and keeps the shoes in top condition. I thought, "Man if this works so well on my shoes I wonder how it will work on my car seats?" Well the Buffalo Butter didn't do anything on my seats. An hour later 100% of the stuff was still there, setting on top of the finish like I had just applied it. I also have a split hide, lamb skin jacket, which is the softest leather I have ever felt. I tested the Buffalo Butter on an inconspicuous location and it turned the leather dark, which it doesn't do on my shoes.
So what's my point? :nixweiss Doing nothing to your car's leather is not good. Car manufacturers don't use the same grade of leather that clothing or furniture manufacturers use. So the care that these products require is not the same that is needed for automobiles nor is the products that should be used the same. The automotive environment is probably the harshest conditions that leather can be subjected to, extreme summer heat and extreme winter cold. This is one of the reasons that most automotive leather is coated with a sealant. Another is for color uniformity across the model line. You could take a seat made for the first car and put it into another vehicle made 5000 units later and it would still match in color and texture. I would say 70% to 80% of the vehicles on the road with leather don't get any leather care and that's the standard that manufacturers use to build their cars to. So, IMO, modern cars have pretty tuff leather interiors. They require very little care to keep them in good shape, but the standards that are applied here at Autopia should keep your leather in peak condition for decades. Don't worry if you don't have anything to treat your leather with right now. You could go months without doing anything and no long term harm will be done so don't rush out and buy the first thing you see on the shelves.
You'll get as many different opinions on what to use on your leather seats as you would on what wax to use. Lexol is okay, but it does leave your seats a little slippery and I don't think it smells too good. I use Pinnacle Leather Conditioner and think it has a nice new leather smell to it, but other people who use it disagree.