I clean and condition my leather seats twice a year in three cars. I've been using this for many years, it works great!!! I have a 12 year old Saab convertible with leather seats with 130K miles, the seats look brand new
I have used various products over they years, but the one I tend to end up going back to is Lexol Leather Conditioner. If it can keep a 60 year old saddle looking great and the leather soft and supple I figure it will do well on the seats as well.