Stop in for a cup of coffee

So, looking at the trans, the input seal looks perfect and still has some greese present. I did see this pipe plug looking like it was loose. I checked a spare trans and this plug is flush. I took it out, cleaned off the Teflon tape, used pipe paste and reinstalled. Now it went flush. Could it be the source of the leak?

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How tight was plug when it came out?
You replacing seal while its out?
I would.
The other possible leaks are pump housing bolts and out the case vent.
Overfilled will cause foaming and it will burp out the vent. It will also foam if the fluid if its low.
I hope the plug solves your issue.