I got a red pen mark on a butter soft sueded jacket - I was sick over it. I actually just got a white pencil eraser and rubbed very lightly to see what would happen. I certainly did not want to make it worse.

It worked fine - red pen mark is gone and suede not marked. I don't know if you will have the same luck with shearling but the shearling coat I have came with a brush/scrubby thing for spots/stains. Maybe try a kitchen scrubber very lightly just to see if it works. Try it first on the flap that turns inside the coat.

Good Luck