Do you know what we are trying to remove - it is no more the mold you talk about, surely it is something else and looks tough or sort of discoloured film.
Have you used a stiffer brush mentioned earlier, maybe Eraser-4 or some wooden skeewers to help peel the unknown off the leather finish.
I do not know exactly how you do it, unless it is by on-time "skype" but the possibilities is still there.
Keep trying other tools - once the Prep-77 penetrates, soften or suspend give it a try with a wooden skeewers and see if you did them out safely.
The next test is with Stripper-2.3, but it may also compromised the original finishing.
Let me know what you think?
