+1.
Although 30 years later, Madison was against secession.
I am not sure if the last reference is the one where he speaks against secession, because I was left with the impression that the context of the discussion concerns nullification. He made the point to me that a state cannot receive the benefits of the national union while concurrently deciding to selectively obey its laws.
In terms of a general right to secede, the 20th century provides an example of peaceful secession with Czechoslovakia and brutal separation with Yugoslavia.
James Madison, Secession, & State Sovereignty
https://groups.google.com/forum/#!topic/alt.war.civil.usa/p5V_C8Hm8yw
Do States Have a Right of Secession?
https://www.capitalismmagazine.com/2002/04/do-states-have-a-right-of-secession/
James Madison on Secession
https://almostchosenpeople.wordpress.com/2010/02/26/james-madison-on-secession/