One stained by body oils, I don't think leather can be cleaned. You might try a carefully-placed shawl to cover the dirty looking spots when you are expecting company.

If it's not suede you can clean it with a moisturizing body wash (I use oil of olay but anyone should work). Mix it with water and dip a cloth in the solution and wring it out really well then scrub away. When you're done go back with another well wrung out damp cloth to "rinse" the soap off. I taught my mom this and she uses it all the time cleaning her vacation rental apartments and it works great. You may have to repeat the process a couple of times just make sure you wring out the cloths well. As far as the oily spot, you probably won't be able to get that out completely, nor do you really want to, oils are good for leather. Get yourself a good leather moisturizer and moisturize the rest of it to match. The faded spot may come back with the moisturizer, your pant legs could have just been trying that spot out more than the rest. If not, a little brown shoe polish may help but I'd do that at your own risk. If it doesn't match it could look worse and if you don't buff it all out you could end up staining the clothes of anyone who sits there. If it was mine I'd try it but that's just me. I've used it on belts and purses and was able to buff it enough that no color came off on my clothes.

Jenica