Might check your adapter for cracks and/or wallored out mounting holes. I had that between my 4l80e and 246 autotrac that had a leaking trans/transfer case seal.
I think all the earlier floor shift transfer cases just take regular ATF. The later push button/auto-trac transfer cases require the blue stuff from GM with friction modifiers for the clutch pack.
I am working on my 6.5 build and stumbled onto this thread. I am considering gapless rings, but doesnt look like Leroy sells them anymore and couldnt find them on Total Seals website eaither. So you can have standard stock rings machined into gapless rings?