The seal on the shaft extending through the transmission extension where it mounts onto the transfer case. I did hear back from Tera Flex this morning and they said they are not sure why it is not showing up on their website but hear is the part number from them https://www.northridge4x4.com/part/...SrkT0R_lgGaf_94_TwIL4Xd-ittriWG0qhujDLzTbJYn6
That’s the seal extension which you need when swapping from a manual to automatic. Not to be confused with the transmission housing extension.