is this possible? Toy related

ya know the kid doodlers - or anything like the doodle pro things - where you can draw and wipe out what you do...

there's ALWAYS a spot or two that just don' go away....is there ANY way to get rid of those? Em has 2 big ones that she loves and a few tiny ones that we use in the car and i have one in the diaper bag and EACH one has at least ONE spot that just doesn't erase....it makes me batty!

figured i'd take a shot to see if anyone knew if it's even possible to fix...