I have heard of folks using it for just this purpose,I believe it was said to only use one quart,so you are mixing it at about 4:1 ratio. The reasonAutomatic tranny fluid in an engine? I'll stick with motor oil. JMO..
On Higher mileage vehicles changing from Dyno/Petro Based oils to synthetic can also cause oil leaks due to its ability to go places where dyno oils do not.