Update: took it in this morning. The shop owner showed me the part that he was going to install. Definitely OEM. The "seal" (dust boot?) at the end had a little crease at the edge, but otherwise it looked good.

Got the car back this evening and the clutch works well. Engages right at the middle of the travel range, a bit of free play near the top but not excessive. Hope this repair holds, and kudos to United for standing behind their work.