What is this part/Where does it go? 440 Rebuild

In my haste to get the cases together before the 1184 had a chance to dry, I failed to notice that this plastic piece had fallen out. I think it goes here at the end of the drive shaft. What is its purpose? Is it essential? I does not seem to want to go back in place with the cases back together. Gracias.

1980 440-Ltd crankcase diagram at Partzilla. 13045-1001 RECEIVER,OIL.

I don't know anything about it.

Thanks for the diagram. That at least gave me the correct orientation to jam it in place. The best I can tell is that it pools oil at the end of the shaft.

Is that a sealer or glue to hold it or is it tore...... I have no idea on it either but I wonder if you outta see about a new one and make sure its on there right .... sounds like it does a important job.