I used the oxy clean/magic eraser method in this thread on several estate pipes I have with vulcanite stems. It worked wonders. Most of the stems were white after a 45 minute or so soak in warm oxy clean water, and the magic eraser did great job of removing the oxidation brought to the surface. I rubbed some olive oil in, then wiped it off a little while later, and they all look as good as new.
I did have an issue with the magic eraser removing the metallic from the Savinelli logo on a couple of stems, but some metallic paste like this fixed that issue:
Amazon.com: Rub N' Buff 1/2oz Antique Gold: Arts, Crafts & Sewing
In the future, I will probably get some stem oil made especially for pipes.