The $300 lesson I learned about cheap parallels for my South Bend 9A

I picked up a set of import parallels off a guy in Cleveland for $40 thinking I got a deal, and they warped on the second week of facing jobs on my old South Bend 9A. The hardened steel was soft enough that my 6 inch vise actually dented the edges, and one pair snapped during a simple aluminum setup when I was only running 1400 RPM. I lost a whole Saturday re dialing in a fixture that should have taken 20 minutes, plus $85 in scrap aluminum stock that ended up in the bin. My neighbor who runs a Haas told me to just bite the bullet on a matched ground set, and honestly he was right. Has anyone else had parallels go soft on them mid job, or is this just bad luck with the import stuff?