HELP (71 Stepside C10)

Need some help. I have tranny leak where the speedometer cable connects to the trans. I have changed out the gear housing and put on a new cable. I used RTV as well and within 10-15 mins I have trans fluid on the ground. I have tried everything, both parts are new. The cable is new from Chevy Resto and gear housing is from Chevy Dealer. The O-ring is new as well, any ideas to help me get this resolved? Thanks in advance for any help out there.

check the seal on the gear housing where the the cable slides in

Tried that and still did not work. Tried several new seals and two gear housing from the chevy dealer. It stopped leaking for about a week and started back as of today.