As you can see the snap ring has worn a groove in the washer. The washer has a flat on the inside and loosely sits in a groove on the hub. That is where the damage is. The hub and washer no longer fit together like they are supposed to.
The year of the trans is what determines the shaft needed, and if I remember it was something like 66 up is one spline and 66 down was another so it shouldn't be too hard to get the right one.
