Very nice find, the black one is probably an old Surgical Black, and may not be glued in. Most of the old ones I have found were glued in by swarf or shrinkage of the box.

Tap the top edge of the box, down on one end with a small hammer. Just a few light taps will break the bond, you will hear the difference in the sound when it breaks loose, light taps are all you need.

I have had great results with 99 Cent Store "Awsome". A couple ounces in a glass pasta jar and water, let it soak, may take a week or so.

Enjoy the pair.