Jetta Automatic transimission problem
 

I just put a used automatic transmission in my 1999 jetta ( new body)
changed filer. etc.... after few months the pan gasket below off and starting leaking transmission fluid , changed the gasket happened again.
spoke with a transmission mechanic , they said the transmission vent is blocked off causing the preassure to below out the gasket.

1) Is this correct?
2) if yes , where is this vent located?

Thanks
Maj