Hi,
That is the transfer input shaft housing O-ring. I looked and found what I believe is the correct part number. To the best of my knowledge, it is 91301-PH8-005. You can get them on Amazon and other places.
Please keep in mind, it will be important to confirm that once you get the part. However, I feel that is the correct part.
See pic below. I highlighted the part I believe you are looking for. Please confirm that for me. Next, when you reinstall the transfer shaft housing, make sure to lubricate the new o-ring to prevent damage prior to installing it.
Let me know.
Joe
Image (Click to make bigger)
Monday, December 14th, 2020 AT 3:06 PM