according to my bookmark, Bug in eval in pre-5.14 shows an example of the bug in practice, and provides a link to perl514delta, directing you to the sections on $@, which explain that prior to 5.14, $@ could be clobbered. I don't know if that's sufficient enough for you and your colleagues.

addendum: that conversation also has an anonymonk-link to a couple of rt issues with verbiage that says it's still dangerous even after 5.14's improvements.