Automatic transmission gasket

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I flushed, changed the filter and added a transmission oil cooler to the 150 d4d prado. The problem is the first gasket split length wise, it was a repco cork one, I think I over tightened it, but not certain. I then used just atf gasket maker, did a bead, put it on and finger tightened it. The next day I nipped them up and filled with oil. It is still weeping at the back, so bought a cork, rubber composite from Toyota. Should I use a sealant, or just use the gasket alone. Any help would be greatly appreciated