I have never had much success with anything marketed as a leather cleaner. I've done full interior-out cleanings to my E36's 4 or 5 times and have tried various products, though none of the expensive/high end(Leatherique, etc) products.
What I will general use now is Mr. Clean Magic Eraser. That stuff really is magic - it'll take scuffs right out of the leather. Just be sure not too scrub too hard, as you do see the leather's color bleeding onto the sponge. Just try to keep the sponge fairly dry so that water does not pour out of it, and you'll instantly see the dirt come off of the seat. Can't recommend them highly enough.
I can't speak for the long term effects on leather, though. I collect vintage/otherwise collectible sneakers(Nike, Air Jordan, etc) and have used Magic Erasers for many pairs over the years, with nothing but amazing results. Never had a
problem using them on the leather of my 1985 Air Jordans, and I personally wouldn't have a second though about using it on my car's seats.