I think Ben Franklin freed a slave or two toward the end of his life and, even began to advocate abolition.
http://commonplace.online/article/benjamin-franklin-slavery/
Benjamin Franklin, Slavery, and the Founders: On the dangers of reading backwards
David Waldstreicher
[Excerpts]
Events after 1776, of course, do matter, as do the final acts of great lives. Franklin lived just long enough for his slaves to run away and die off, and for antislavery to become politically safe in his home state. ...He did not so much experience a sea change in his attitudes as he managed to deflect the blame, deflecting criticisms of the Americans as slavemongers into a critique of colonialism British style, establishing a common ground in favor of liberty—and the American cause. ...
Franklin’s antislavery credentials have been, at the very least, remembered backwards. At most, they have been greatly exaggerated. ...
He owned a series of slaves between about 1735 and 1781 and never systematically divested himself of them. ...
There are enough smoking guns, to be sure, to condemn Franklin as a hypocrite, Jefferson style, if one wishes to do so.
In 1758, Franklin took two of his slaves, Peter and King, to England. King ran away and took freedom in England. I know of no evidence of Franklin having manumitted his slaves.
I read the article you linked. It is a good read.
Perhaps this line from the article helps to justify why I got things so wrong in my post 92: “We need to remember what Franklin helped Americans to forget, how he did so, and why.”