I think it's broadly Composition Rust Preventive. I suppose Corrosion-X Rust Preventive is another candidate.
Figure to leave it in for an hour. Should be more than enough time to equilibrate. If that doesn't let you pull it loose, take a Styrofoam box and pick up some dry ice. Set a cloth pad on it (to prevent thermal shock) and set the die on the pad and put the lid on and go away for an hour.
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