I love the Mr. Clean Magic Eraser. Love it. It's the only thing that gets scuff marks off paint without removing or discoloring the paint. I use it for everything.
And I discovered its ultimate purpose. Lego + Sharpie = garbage. Most of the time. I tried scrubbing off marks with a kitchen sponge but all that did was scratch the plastic. I also tried a few other chemical approaches but they never got the Lego completely clean.
Until I tried the Magic Eraser. It was effortless.
My trusty assistant helped me with this video - as you can see, he's not scrubbing hard (but he did have trouble holding the brick steady - I should have used a bigger one) and it only took a few seconds.