I used a wire handled bluing applicator (has a spherical head of a soft material) from a Birchwood Casey kit (http://sport.birchwoodcasey.com/Fini...e-ce5162d90f89
) chucked in a variable speed drill with Mother's Mag polish.
You want to use a gentle polish like Mothers, Flitz or something similar, not a grinding compound that is going to take off a bunch of metal. I think the red polish they give you in a Dremel kit is probably too aggressive. Do it slow and easy, it doesn't take a lot of effort.
It seems that people who are buying 938s from later in production are having fewer issues, you may not need to do anything to it.