So I had the TH400/NP208 Adapter replaced today on my '84 M1028.....see pics below.....no big surprise that Dexron III would be leaking through that large a crack!
Per my transmission shop, there simply is an O-ring between the adapter and the TH400, and then a gasket between the adapter and the NP208, and this is what seals the ATF within the transmission system......there is no output shaft seal on the TH400 that would seal off ATF from the void in the adapter......ATF that is in the void of the adapter is in common with the ATF in the transmission pan. There is a seal in the front of the transfer case that seals off its Dexron III within the transfer case, and my transfer case seal was fine, so the source of my ATF leak at the adapter was from the transmission system fluid flowing out the cracked adapter.
No idea what/why/how the adapter was so severely cracked, but it's fixed now.....my first experience ever with this issue so I learned a lot.
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