I looked at the reference works on hand for Galatians spanning 150 years and didn’t find any reference to A.Ag 953, not even in H.A.W. Meyer or Henry Alford, the most likely to cite classics. I also checked TDNT, EDNT, Grimm-Thayer, Spicq. Every one who cited classics mentioned S.Aj 944, some also mentioned E.Or. 1330, Pl.Ep. 8.354d. Aeschylus was ignored even though the citation from Euripides looks like it might have been borrowed from A.Ag 1070.
As far as I know and could verify in dictionnaries, the ‘yoke of slavery’ isn’t a Homeric image; for Homer, slavery is the ‘day of slavery’. According to LSJ ζυγόν I.2., ‘yoke of slavery’ exists in Hdt 7.8. (Herodotus? Didn’t actually look that up), so maybe in Attic it’s not completely restricted to tragedy. But as far as I know, Agamemnon is the earliest of the references in LSJ.
Of course it’s surprising if works on the NT cite other tragedians as parallels, but not Aeschylus, who is the earliest.
A little googeling turned up a citation of A.Ag 953 in Henry Alford (Greek Testament) in his notes on 1Cor. 7:21 page 521 col. 1. Kind of surprised he cites it here but not under Gal 5:1. At least someone was talking about it in the 19th century. One of the reasons it doesn’t show up now is that it isn’t cited in LSJ under ζῠγόν:
LSJ @ UChicago
δούλιον ζ . the yoke of slavery, Hdt.7.8 . γ, A.Th.75 (pl.), 471, etc.; δουλείας, ἀνάγκης ζ., S.Aj.944, E.Or.1330;
A citation of A.Ag 953 also turns up in a book published in the Corinth Greece 1987:
Peter Marshall, > Enmity in Corinth: social conventions in Paul’s relations with the Corinthians> Mohr Siebeck, 1987, page 299, n. 82.
It is indeed, Clayton, a nice, clean parallel. It is also illustrative of the GNT tendency to prefer nouns in the genitive standing in for adjectives, which seem to be more popular in Homer and classical Attic.
“Were you called a slave? Let it not be a concern to you. Rather, even if you are able to become free, instead, all the more, make use of (your slavery.”)
This is a famous crux, whether the object of χράομοι is freedom or slavery. Is Paul saying, contra Aeschylus, that the Christian DOES deal with, DOES make use, DOES willingly take on the yoke of slavery?
Henry Alford[1] has a comment somewhat along those lines. On the other hand ζυγόν doesn’t appear in this co-text, only in Gal. 5:1, 1Tim 6:1 of the Pauline books.
[1] a citation of A.Ag 953 in Henry Alford (Greek Testament) in his notes on 1Cor. 7:21 page 521 col.1.