Quick question about the s13 5 speed trans

[Dsmguy1993]

So I had a spare s13 ka trans laying around that I eventually wanted to get to rebuilding. Anyways I took apart the tail and bellhousing off of this transmission and I just have one quick question. There is a little circular piece in this picture below the gear not sure if thats some type of dowel or what but it appears to be damaged anybody know what that thing is?

https://ibb.co/vxJQDNN

[NukeKS14]

https://www.nicoclub.com/nissan-service-manuals

[Dsmguy1993]

If you look at my picture notice how in the bottom left hand corner there is a dowel pin next to the bolt holes now diagonally up to the right from that dowel you see this small circular piece that is in two sections with a slit between it halfway what is that? I appreciate you linking me to the fsm but I dont know if the fsm will tell me what that is and also I cant even find the fsm for this transmission the way i took it apart was remove the shifter pins, remove the front bellhousing cover take the snaprings out then put the trans bellhousing down tap off the tail a bit and then put it back down and tap off the bellhousing all the way and last The tail slides right off. Obviously removing the mid section bolts as well.