Sarah,
What type of leather is it?
Pigmented, Aniline or Nubuck?
Most common leather is pigmented, therefore you are cleaning the coating on the leather. Too much solvent in the wrong hands can start breaking this down. You end up with a bigger problem than you started with. More importantly the problem is now yours. If it's Aniline or Nubuck probably it won't shift.
You would be best off speaking to someone who is trained and has experience in leather repairs.
Regards
Nigel