“Many have pointed out that the Articles of Confederation’s reference to “perpetual union” was replaced in the Constitution by a “more prefect union”.”
That’s what I thought, the term perpetual union does not appear in the Constitution.
Adopted in 1777, the “perpetual union” lasted just 12 years and was then replaced by the Constitution.
The term “perpetual union” was an aspiration of the people who used the term; it was not a binding revelation of duty to future generations unless they wanted it. They didn’t.
Another example: the federal law named the “Affordable Care Act”. That too is a stated aspiration, but because it is not affordable, it is not sustainable and it is going away. Hopefully, it will go away peacefully.
Replaced totally peacefully in 1788 by mutual consent, the second of the two legitimate reasons for disunion.
The first reason, as in 1776, is necessity brought on by a long list of oppressions and usurpations (see Declaration of Independence).
Neither condition existed in 1861, so Deep South Fire Eaters declared their secessions at pleasure for which they had no support from our Founders' ideals.