transmission self destruction as foaming will occur if the oil level is too
high, rectify it immediately. Tell the moron that over filled it to choose
another job.

The reason transmission should not be overfilled is that the oil level
rises to the spinning parts which then fling it about aerating the oil.
So, what's bad about that? The transmission uses hydraulic pressure to
clamp its clutches and bands etc.; air compresses and the hydraulic
pressure can be compromised and so allow the clutches to slip during
driving.

Correct level is found with transmission hot, engine at idle, car level
and gear in Park. Level should be between the two marks on the dip stick
and not above or below that range.

I suggest you do a trans service at this time... get rid of all old fluid...
drain, refill, drive a while for 2 times before you drop the pan and replace
filter... then refill to proper level and tranny problem should all
disappear.