If the case is made of smooth leather (no suede!), then saddle soap is a good way to clean the surface. It consists mainly of glycerin. Afterwards, use leather grease (according to LEO, it's translated "dubbin") to feed the leather again.
Saddle soap is basically just pure soap made of glycerine, and easily used. You use a soft sponge, wet it and squeeze most of the water out. Rub a little over the soap, then rub a lot across the leather. When drying, a little white foam might show up - polish it out. So it's rubbing, rubbing and then again some rubbing
I use these to clean my car's leather seats as well. It's really a lot of work this way, but the leather will look much better afterwards. Those "magic chemicals" promise more than they are good for, and can mess with the colour.
I've been using the stuff from PepBoys for your car... I'm sure it's fine. I believe it's Black Magic Leather Cleaner and Conditioner. Spray it on a cotton cloth and rub away.
You may not believe this but I've been using this on my instroke for 5 years.Its made from pine tar and beeswax.Been around since 1929.It works great! It will darken light colored leather but I really liked what it did to mine. Turned it from light brown to the color of honey. Softens and waterproofs.Rub it in with your fingers and wipe it down with a clean cloth. It also takes the smell of smoke out. I use it on my bomber jacket too.