I've been back and forth on it, but in the end I'm more comfortable disclosing it. I think Southwest specifies not to include UPT stage checks, but for the rest of them I mark it and provide an explanation. With all of the hiring going on I think there's more to lose from not disclosing it than there is from putting something that happened over a decade ago on the app with plenty of experience to overcome the slight black mark.
Just have a good answer prepared for the interview about how it was actually your form partner's fault or your instructor's fault or whatever. (joking of course!)