727 trans leak

Dumbass me overfilled (apparently) the trans last week. Didn't notice any leaks until Tuesday this week, when I saw trans fluid all over the garage floor. It seems to be coming out of the O ring at the fill tube. If I overfilled it, will it cause it to leak like this, or is the O ring just bad? I have never owned a car that didn't have a clutch.
I can't run the engine to check the fluid because I don't have a battery for the car. I can use my truck battery tomorrow, but if the trans is overfilled, will starting it to check the fluid do any damage?
Thanks for the help.

Author: admin