[AK72K10]

My 1972 K10 has a transmission leak. The pan had some kind of reddish-orange silicone bead around a rubber gasket that was leaking, but I removed that, scraped off the gunk, checked the pan for burrs/dents/distortion, and replaced the old gasket with a new cork gasket. Alternately torqued down the bolts supporting the pan, taking care not to over-torque, and refilled with ATF (MD3). Let the truck cool down, sitting overnight, and found that next morning it was leaking once again, with a significant pool on my garage floor. Checked the plug and it was dry, but found ATF all around the seal. Have been told to stay clear of rubber, not to use cork, and all kinds of different things but want to get the answer from people in the know so I am posting the question to you. Where am I going wrong here? What is the best gasket to use? Any guidance you might be able to provide would be greatly appreciated.
Thanks,
AK