Unfortunately, you might not be able to get the stain out because it sounds like it's already set into the leather. With oily liquids (like lotion), removing the spill as soon as possible is the best way to ensure it doesn't leave a lasting mark. You could try an Autoglym leather cleaner: www.amazon.co.uk/Autoglym-AG-215007-Leather-Cleane...C

You should also try Googling some home remedies as well - a lot of people recommend things like lemon juice but we haven't tried that.