Aramaic Wordplay in Luke 14:5?

I'm still plugging along in Casey's Aramaic Sources of Mark's Gospel. I observe that he approves (p. 30) of Matthew Black's hypothesis of Aramaic wordplay at the origin of Luke 14:5. Here's the text of the NIV with the proposed Aramaic originals in parentheses: “If one of you has a son (bar) or an ox (be'ir) that falls into a well (ber) on the Sabbath day, will you not immediately pull him out?”

Casey calls this "perfectly plausible." There are at least two problems with this theory. One is that be'ir (בעיר) is not the Aramaic word for "ox," which is tor (תור). Be'ir just means "livestock, large domestic animal," and could include other animals as well as oxen. One of Casey's methodological principles is that one should not just translate backwards to get at the original Aramaic, but also ask how a suggested Aramaic original would have likely been translated. In this case, I think that be'ir would surely have been rendered as ktenos, not as bous, which is what the Lukan text has. Bous most reasonably points back to tor, and that dissolves the wordplay.

That's one problem. Another one is the textual problem in this verse. For "son" (huios) in the Nestle-Aland critical text, the Textus Receptus has "ass" (onos), which is supported by Sinaiticus, among others. "Son" looks to be better attested; on the other hand, "son" spoils the a fortiori argument apparently used by Christ in this verse (compare the similar story in Matt. 12:9-13): If animal, why not human? On the other hand, perhaps the argument is not a fortiori, but a maiori ad minus; since the custom allows the greater breach of Sabbath law, it should allow the lesser: If lifting, why not healing? It's a toss-up, and the textual decision is interwoven with the exegetical choice.

A remote possibility is that the original Aramaic (if there was such a thing) read bar torin, calf, literally, "son of oxen," and that this somehow made it into the Gospel as "son or ox" (bar o tor). I doubt that's what happened, but I mention it for the sake of completeness.