I don't recomend using silicone.
One product I have always liked is Tanner's Preserve, they sell two different products, one is a cleaner, the other is a treatment/dressing. If you can find them, first clean then treat them following the instructions. One thing to remeber about leather is that there are many different kinds of leather, for different applications. Some leathers are intended to be shiny, others aren't, which is part f how they make the stuff from the hide into the finished product.