Ya, honestly....the old car-wash tx. and then drive it a bit. It also helps to find oil leaks by going under there in the absolute darkness of night and use a beam flashlight. That way, you only see what you are looking for. I do it all the time......seriously.
Slight output shaft seal leaks never disrupt my life. I just check the trans level rather frequently. And, yes, I have pretty nice concrete here at the place. Lucas did his best to get brake fluid all over it when he was here.........YUCK!