Few questions...
-How long has the gum been stuck to the leather? Is it still sticky, or almost dried hard?
-What kind of leather? I know that some of the newer MB's are coming with uncoated full analine leather. Scratch the leather, does it get any lighter where you scratch? If yes, its uncoated.
-Where on the leather is the gum? Seams? Perforated section?
Either way, you're gonna need to be careful with this. First, remove as much of the gum as you can by hand. I use toothpics to help with prying it off. Next I mix a strong solution of woolite/water and swab the leftover gum/leather with q-tips. Ill let that soak, then I get to removing the leftover gum again with toothpics and patience.
There may be other fasters ways, but just remember patience is your best friend with this.