The Dexron* III Mercon type of ATF is a superior lubricant that has sheer resistant properties not available in typical hobby lubes. It's ability to withstand heat is immaterial and irrelevant.
Dexron III Mercon is safe for transmissions with plastic-cased sending units, and that is where it is used. It is also safe for hobby paints. I have inadvertently left smudges of ATF on some of my Pennsy tenders and was able to rub it off days later with no ill effect.
*I mistakenly added a T to my earlier post's spelling of Dexron.