A quick google search indicates there is a credible school of thought that says use ATF.
If someone posts that ATF will make the plates come apart they should relate their personal experience or other proof. Otherwise it should be qualified as an opinion and not as a matter of fact.
IMO
I did a Google search on Barnett Instructions and was totally frustrated. Some say soak in oil, some say soak in ATF, some say soak in the fluid that they will run in (oil for Japs, ATF for Harley's, Trumpets, things with primary cases using ATF, etc) and some say don't soak at all as the plates were made to run wet or dry.
So, you're on your own. Personally, I'd rub a little MC motor oil on them and slap them in. Personal first hand experience. Worked for me.