Sunder has been nudging me to get mine fixed, but I confess that I put gear lube in mine when I topped it off once and then changed the oil and put just gear oil in.... I don't know what it is going to be like to flush it and eventually use nothing but ATF.

Do the internal inspection that keeps being pushed. It won't hurt anything and you will get to see the inside of your 231. You are lucky to have a spare in case it is tore up inside, right?

It isn't all that hard to flush. If it feels/smells like gear oil, nothing too big to worry about. If it feels like transmission fluid and smells like burnt ATF, then you may have to worry and wonder why it was pulled in the first place.

Good luck!