I think this comes down to a semantic discussion of seals and gaps. Magnetism will provide a force that if generated by an electromagnet can attract or repel as desired. The quality of the seal and any gap formed will become a factor of the smoothness or uniformity of the two mating surfaces, the uniformity of the forces on the two surfaces and how the distance between the two surfaces can be maintained. Certainly a magnetic field can be the origin of some of these forces. But meeting the 3μ gap requirement will be dominated by factors other than magnetic fields.
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"Don't disturb my circles." translation of Archimedes last words
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