I can try to help you if you can provide more info: Do you know the type of leather= aniline dye, corrected grain, bycast or? What climate region you live in? Have you removed any of the foam or fiber in the cushions to check where the odor is coming from? Can you describe the odor?
Its a little bit unusual for a odor to develop sometime after the purchase thats directly related to the leather itself.

Unfortunately, I don't have a clue as to what type of leather our sofa is made of. We live in California. I am not able to describe the odor(more towards rooms with old carpet etc but I know I could be way off). Initially, I even suspected the presence of mold in the room and went to the extent of hiring a mold inspector to do the testing. The mold spore count was way too low and we figured that was not the problem. Is it possible to check on the fiber of the sofa without tearing it. BTW, I noticed and there is a small area in the loveseat which is torn. When I go near the sofa I am not able to point out where the odor is coming from. However, we go out and come back to the house, I can smell the odor.